diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/planner/chart/ContiguousDaysLine.java b/navalplanner-business/src/main/java/org/navalplanner/business/planner/chart/ContiguousDaysLine.java
index 7940cd3ab..9b606916f 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/planner/chart/ContiguousDaysLine.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/planner/chart/ContiguousDaysLine.java
@@ -18,15 +18,23 @@
  */
 package org.navalplanner.business.planner.chart;
 
+import java.lang.reflect.Array;
 import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
 import java.util.Iterator;
+import java.util.LinkedList;
 import java.util.List;
 import java.util.ListIterator;
+import java.util.SortedMap;
+import java.util.TreeMap;
 
 import org.apache.commons.lang.Validate;
 import org.joda.time.Days;
 import org.joda.time.LocalDate;
 import org.navalplanner.business.planner.chart.ContiguousDaysLine.ONDay;
+import org.navalplanner.business.planner.entities.DayAssignment;
+import org.navalplanner.business.workingday.EffortDuration;
 
 /**
  * It represents some contiguous days from a start date to a not included end
@@ -75,12 +83,154 @@ public class ContiguousDaysLine<T> implements Iterable<ONDay<T>> {
         return new ContiguousDaysLine<T>(fromInclusive, daysBetween.getDays());
     }
 
+    public static ContiguousDaysLine<List<DayAssignment>> byDay(
+            Collection<? extends DayAssignment> assignments) {
+        if (assignments.isEmpty()) {
+            return invalid();
+        }
+        DayAssignment min = Collections.min(assignments,
+                DayAssignment.byDayComparator());
+        DayAssignment max = Collections.max(assignments,
+                DayAssignment.byDayComparator());
+        ContiguousDaysLine<List<DayAssignment>> result = create(min.getDay(),
+                max.getDay().plusDays(1));
+        result.transformInSitu(new IValueTransformer<List<DayAssignment>, List<DayAssignment>>() {
+
+            @Override
+            public List<DayAssignment> transform(LocalDate day,
+                    List<DayAssignment> previousValue) {
+                return new LinkedList<DayAssignment>();
+            }
+        });
+        for (DayAssignment each : assignments) {
+            result.get(each.getDay()).add(each);
+        }
+        return result;
+    }
+
+    public static <T> ContiguousDaysLine<T> invalid() {
+        return new ContiguousDaysLine<T>(null, 0);
+    }
+
+    @SuppressWarnings("unchecked")
+    public static ContiguousDaysLine<EffortDuration> min(
+            ContiguousDaysLine<EffortDuration> a,
+            ContiguousDaysLine<EffortDuration> b) {
+        return join(EffortDuration.class, minTransformer(), a, b);
+    }
+
+    public static IValueTransformer<EffortDuration[], EffortDuration> minTransformer() {
+        return new IValueTransformer<EffortDuration[], EffortDuration>() {
+
+            @Override
+            public EffortDuration transform(LocalDate day,
+                    EffortDuration[] previousValue) {
+                return EffortDuration.min(previousValue);
+            }
+        };
+    }
+
+    /**
+     * Joins both {@link ContiguousDaysLine} substracting from minuend line. An
+     * effortDuration can't be negative so, if subtrahend line is at some point
+     * bigger than minuend, zero is returned at that point.
+     *
+     * @param minuend
+     * @param subtrahend
+     * @return
+     */
+    @SuppressWarnings("unchecked")
+    public static ContiguousDaysLine<EffortDuration> substract(
+            ContiguousDaysLine<EffortDuration> minuend,
+            ContiguousDaysLine<EffortDuration> subtrahend) {
+        return join(EffortDuration.class, substractTransformer(), minuend,
+                subtrahend);
+    }
+
+    private static IValueTransformer<EffortDuration[], EffortDuration> substractTransformer() {
+        return new IValueTransformer<EffortDuration[], EffortDuration>() {
+
+            @Override
+            public EffortDuration transform(LocalDate day,
+                    EffortDuration[] previousValue) {
+                EffortDuration result = previousValue[0];
+                for (int i = 1; i < previousValue.length; i++) {
+                    result = result.minus(EffortDuration.min(previousValue[i],
+                            result));
+                }
+                return result;
+            }
+        };
+    }
+
+    @SuppressWarnings("unchecked")
+    public static ContiguousDaysLine<EffortDuration> sum(
+            ContiguousDaysLine<EffortDuration> summandA,
+            ContiguousDaysLine<EffortDuration> summandB) {
+        return join(EffortDuration.class, additionTransformer(), summandA,
+                summandB);
+    }
+
+    public static SortedMap<LocalDate, EffortDuration> toSortedMap(
+            ContiguousDaysLine<EffortDuration> line) {
+        SortedMap<LocalDate, EffortDuration> result = new TreeMap<LocalDate, EffortDuration>();
+        for (ONDay<EffortDuration> each : line) {
+            result.put(each.getDay(), each.getValue());
+        }
+        return result;
+    }
+
+    private static IValueTransformer<EffortDuration[], EffortDuration> additionTransformer() {
+        return new IValueTransformer<EffortDuration[], EffortDuration>() {
+
+            @Override
+            public EffortDuration transform(LocalDate day,
+                    EffortDuration[] previousValue) {
+                return EffortDuration.sum(previousValue);
+            }
+        };
+    }
+
+    public static <T, R> ContiguousDaysLine<R> join(final Class<T> klass,
+            final IValueTransformer<T[], R> transformer,
+            final ContiguousDaysLine<T>... lines) {
+        if (lines[0].isNotValid()) {
+            return invalid();
+        }
+        LocalDate start = lines[0].getStart();
+        LocalDate endExclusive = lines[0].getEndExclusive();
+        for (ContiguousDaysLine<T> each : lines) {
+            Validate.isTrue(each.getStart().equals(start),
+                    "the start of all lines must be same date");
+            Validate.isTrue(each.getEndExclusive().equals(endExclusive),
+                    "the start of all lines must be same date");
+        }
+        ContiguousDaysLine<R> result = ContiguousDaysLine.create(start,
+                endExclusive);
+        result.transformInSitu(new IValueTransformer<R, R>() {
+
+            @Override
+            public R transform(LocalDate day, R previousValue) {
+                return transformer.transform(day, getValues(day, lines));
+            }
+
+            private T[] getValues(LocalDate day, ContiguousDaysLine<T>... lines) {
+                @SuppressWarnings("unchecked")
+                T[] result = (T[]) Array.newInstance(klass, lines.length);
+                for (int i = 0; i < result.length; i++) {
+                    result[i] = lines[i].get(day);
+                }
+                return result;
+            }
+        });
+        return result;
+    }
+
     private final LocalDate startInclusive;
 
     private final List<T> values;
 
     private ContiguousDaysLine(LocalDate start, int size) {
-        Validate.notNull(start);
         this.startInclusive = start;
         this.values = new ArrayList<T>(size);
         for (int i = 0; i < size; i++) {
@@ -88,12 +238,23 @@ public class ContiguousDaysLine<T> implements Iterable<ONDay<T>> {
         }
     }
 
+    public boolean isNotValid() {
+        return startInclusive == null;
+    }
+
     public LocalDate getStart() {
+        mustBeValid();
         return startInclusive;
     }
 
+    private void mustBeValid() {
+        if (isNotValid()) {
+            throw new IllegalStateException("this line is invalid");
+        }
+    }
+
     public LocalDate getEndExclusive() {
-        return startInclusive.plusDays(values.size());
+        return getStart().plusDays(values.size());
     }
 
     public T get(LocalDate day) throws IndexOutOfBoundsException {
@@ -137,6 +298,9 @@ public class ContiguousDaysLine<T> implements Iterable<ONDay<T>> {
 
     public <R> ContiguousDaysLine<R> transform(
             IValueTransformer<T, R> doubleTransformer) {
+        if (isNotValid()) {
+            return invalid();
+        }
         ContiguousDaysLine<R> result = ContiguousDaysLine.create(
                 startInclusive, getEndExclusive());
         for (ONDay<T> onDay : this) {
@@ -146,6 +310,34 @@ public class ContiguousDaysLine<T> implements Iterable<ONDay<T>> {
         return result;
     }
 
+    public ContiguousDaysLine<T> copy() {
+        return transform(ContiguousDaysLine.<T> identity());
+    }
+
+    private static <T> IValueTransformer<T, T> identity() {
+        return new IValueTransformer<T, T>() {
+
+            @Override
+            public T transform(LocalDate day, T previousValue) {
+                return previousValue;
+            }
+        };
+    }
+
+    public static <T, S, R> IValueTransformer<T, R> compound(
+            final IValueTransformer<T, S> first,
+            final IValueTransformer<S, R> last) {
+
+        return new IValueTransformer<T, R>() {
+
+            @Override
+            public R transform(LocalDate day, T previousValue) {
+                S intermediateValue = first.transform(day, previousValue);
+                return last.transform(day, intermediateValue);
+            }
+        };
+    }
+
     @Override
     public Iterator<ONDay<T>> iterator() {
         final Iterator<T> iterator = values.iterator();
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/planner/chart/ResourceLoadChartData.java b/navalplanner-business/src/main/java/org/navalplanner/business/planner/chart/ResourceLoadChartData.java
index 9696a006c..943dfa13b 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/planner/chart/ResourceLoadChartData.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/planner/chart/ResourceLoadChartData.java
@@ -21,21 +21,23 @@
 
 package org.navalplanner.business.planner.chart;
 
+import static org.navalplanner.business.planner.chart.ContiguousDaysLine.compound;
+import static org.navalplanner.business.planner.chart.ContiguousDaysLine.sum;
+import static org.navalplanner.business.planner.chart.ContiguousDaysLine.toSortedMap;
 import static org.navalplanner.business.workingday.EffortDuration.min;
-import static org.navalplanner.business.workingday.EffortDuration.zero;
 
 import java.util.Collection;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Set;
 import java.util.SortedMap;
-import java.util.TreeMap;
 
 import org.joda.time.LocalDate;
-import org.navalplanner.business.calendars.entities.ICalendar;
 import org.navalplanner.business.hibernate.notification.PredefinedDatabaseSnapshots;
+import org.navalplanner.business.planner.chart.ContiguousDaysLine.IValueTransformer;
 import org.navalplanner.business.planner.entities.DayAssignment;
 import org.navalplanner.business.resources.entities.Resource;
 import org.navalplanner.business.workingday.EffortDuration;
@@ -60,25 +62,113 @@ public class ResourceLoadChartData implements ILoadChartData {
     private SortedMap<LocalDate, EffortDuration> availability;
 
     public ResourceLoadChartData(List<DayAssignment> dayAssignments, List<Resource> resources) {
-        SortedMap<LocalDate, Map<Resource, EffortDuration>> map =
-            groupDurationsByDayAndResource(dayAssignments);
-        this.load = calculateResourceLoadPerDate(map);
-        this.overload = calculateResourceOverloadPerDate(map);
-        if(load.keySet().isEmpty()) {
-            this.availability = new TreeMap<LocalDate, EffortDuration>();
-        }
-        else {
-            this.availability = calculateAvailabilityDurationByDay(
-                    resources, load.firstKey(), load.lastKey());
-        }
 
-        for (LocalDate day : this.overload.keySet()) {
-            EffortDuration overloadDuration = this.overload
-            .get(day);
-            EffortDuration maxDuration = this.availability.get(day);
-            this.overload.put(day,
-                    overloadDuration.plus(maxDuration));
-        }
+        ContiguousDaysLine<List<DayAssignment>> assignments = ContiguousDaysLine
+                .byDay(dayAssignments);
+
+        ContiguousDaysLine<EffortDuration> load = assignments
+                .transform(extractLoad());
+
+        ContiguousDaysLine<EffortDuration> overload = assignments
+                .transform(extractOverload());
+
+        ContiguousDaysLine<EffortDuration> availabilityOnAllResources = assignments
+                .transform(extractAvailabilityOnAllResources(resources));
+
+        this.load = toSortedMap(ContiguousDaysLine.min(load,
+                availabilityOnAllResources));
+        this.overload = toSortedMap(sum(overload, availabilityOnAllResources));
+        this.availability = toSortedMap(availabilityOnAllResources);
+    }
+
+    private IValueTransformer<List<DayAssignment>, EffortDuration> extractOverload() {
+        return compound(effortByResource(), calculateOverload());
+    }
+
+    private IValueTransformer<List<DayAssignment>, Map<Resource, EffortDuration>> effortByResource() {
+        return new IValueTransformer<List<DayAssignment>, Map<Resource, EffortDuration>>() {
+
+            @Override
+            public Map<Resource, EffortDuration> transform(LocalDate day,
+                    List<DayAssignment> previousValue) {
+                Map<Resource, List<DayAssignment>> byResource = DayAssignment
+                        .byResource(previousValue);
+                Map<Resource, EffortDuration> result = new HashMap<Resource, EffortDuration>();
+                for (Entry<Resource, List<DayAssignment>> each : byResource
+                        .entrySet()) {
+                    result.put(each.getKey(),
+                            DayAssignment.sum(each.getValue()));
+                }
+                return result;
+            }
+        };
+    }
+
+    private IValueTransformer<Map<Resource, EffortDuration>, EffortDuration> calculateOverload() {
+        return new IValueTransformer<Map<Resource, EffortDuration>, EffortDuration>() {
+
+            @Override
+            public EffortDuration transform(LocalDate day,
+                    Map<Resource, EffortDuration> previousValue) {
+
+                final PartialDay wholeDay = PartialDay.wholeDay(day);
+                return EffortDuration.sum(previousValue.entrySet(),
+                        new IEffortFrom<Entry<Resource, EffortDuration>>() {
+
+                            @Override
+                            public EffortDuration from(
+                                    Entry<Resource, EffortDuration> each) {
+                                EffortDuration capacity = calendarCapacityFor(
+                                        each.getKey(), wholeDay);
+                                EffortDuration assigned = each.getValue();
+                                return assigned.minus(min(capacity, assigned));
+                            }
+                        });
+            }
+        };
+    }
+
+    private IValueTransformer<List<DayAssignment>, EffortDuration> extractLoad() {
+        return new IValueTransformer<List<DayAssignment>, EffortDuration>() {
+
+            @Override
+            public EffortDuration transform(LocalDate day,
+                    List<DayAssignment> previousValue) {
+                return DayAssignment.sum(previousValue);
+            }
+        };
+    }
+
+    private IValueTransformer<List<DayAssignment>, EffortDuration> extractAvailabilityOnAssignedResources() {
+        return new IValueTransformer<List<DayAssignment>, EffortDuration>() {
+
+            @Override
+            public EffortDuration transform(LocalDate day,
+                    List<DayAssignment> previousValue) {
+                Set<Resource> resources = getResources(previousValue);
+                return sumCalendarCapacitiesForDay(resources, day);
+            }
+
+            private Set<Resource> getResources(List<DayAssignment> assignments) {
+                Set<Resource> resources = new HashSet<Resource>();
+                for (DayAssignment dayAssignment : assignments) {
+                    resources.add(dayAssignment.getResource());
+                }
+                return resources;
+            }
+        };
+    }
+
+    private IValueTransformer<List<DayAssignment>, EffortDuration> extractAvailabilityOnAllResources(
+            final List<Resource> resources) {
+        return new IValueTransformer<List<DayAssignment>, EffortDuration>() {
+
+            @Override
+            public EffortDuration transform(LocalDate day,
+                    List<DayAssignment> previousValue) {
+                return sumCalendarCapacitiesForDay(resources, day);
+            }
+        };
     }
 
     public SortedMap<LocalDate, EffortDuration> getLoad() {
@@ -130,140 +220,7 @@ public class ResourceLoadChartData implements ILoadChartData {
         };
     }
 
-    private SortedMap<LocalDate, Map<Resource, EffortDuration>> groupDurationsByDayAndResource(
-            List<DayAssignment> dayAssignments) {
-        SortedMap<LocalDate, Map<Resource, EffortDuration>> map =
-                new TreeMap<LocalDate, Map<Resource, EffortDuration>>();
-
-        for (DayAssignment dayAssignment : dayAssignments) {
-            final LocalDate day = dayAssignment.getDay();
-            final EffortDuration dayAssignmentDuration = dayAssignment
-                    .getDuration();
-            Resource resource = dayAssignment.getResource();
-            if (map.get(day) == null) {
-                map.put(day, new HashMap<Resource, EffortDuration>());
-            }
-            Map<Resource, EffortDuration> forDay = map.get(day);
-            EffortDuration previousDuration = forDay.get(resource);
-            previousDuration = previousDuration != null ? previousDuration
-                    : EffortDuration.zero();
-            forDay.put(dayAssignment.getResource(),
-                    previousDuration.plus(dayAssignmentDuration));
-        }
-        return map;
-    }
-
-    private SortedMap<LocalDate, EffortDuration> calculateResourceLoadPerDate(
-            SortedMap<LocalDate, Map<Resource, EffortDuration>> durationsGrouped) {
-        SortedMap<LocalDate, EffortDuration> map = new TreeMap<LocalDate, EffortDuration>();
-
-        for (LocalDate date : durationsGrouped.keySet()) {
-            EffortDuration result = zero();
-            PartialDay day = PartialDay.wholeDay(date);
-            for (Resource resource : durationsGrouped.get(date).keySet()) {
-                ICalendar calendar = resource.getCalendarOrDefault();
-                EffortDuration workableTime = calendar.getCapacityOn(day);
-                EffortDuration assignedDuration = durationsGrouped.get(
-                        day.getDate()).get(resource);
-                result = result.plus(min(assignedDuration, workableTime));
-            }
-
-            map.put(date, result);
-        }
-        return map;
-    }
-
-    protected abstract class EffortByDayCalculator<T> {
-        public SortedMap<LocalDate, EffortDuration> calculate(
-                Collection<? extends T> elements) {
-            SortedMap<LocalDate, EffortDuration> result = new TreeMap<LocalDate, EffortDuration>();
-            if (elements.isEmpty()) {
-                return result;
-            }
-            for (T element : elements) {
-                if (included(element)) {
-                    EffortDuration duration = getDurationFor(element);
-                    LocalDate day = getDayFor(element);
-                    EffortDuration previous = result.get(day);
-                    previous = previous == null ? zero() : previous;
-                    result.put(day, previous.plus(duration));
-                }
-            }
-            return result;
-        }
-
-        protected abstract LocalDate getDayFor(T element);
-
-        protected abstract EffortDuration getDurationFor(T element);
-
-        protected boolean included(T each) {
-            return true;
-        }
-    }
-
-    private SortedMap<LocalDate, EffortDuration> calculateResourceOverloadPerDate(
-            SortedMap<LocalDate, Map<Resource, EffortDuration>> dayAssignmentGrouped) {
-        return new EffortByDayCalculator<Entry<LocalDate, Map<Resource, EffortDuration>>>() {
-
-            @Override
-            protected LocalDate getDayFor(
-                    Entry<LocalDate, Map<Resource, EffortDuration>> element) {
-                return element.getKey();
-            }
-
-            @Override
-            protected EffortDuration getDurationFor(
-                    Entry<LocalDate, Map<Resource, EffortDuration>> element) {
-
-                final PartialDay day = PartialDay.wholeDay(element.getKey());
-
-                return EffortDuration.sum(element.getValue().entrySet(),
-                        new IEffortFrom<Entry<Resource, EffortDuration>>() {
-
-                            @Override
-                            public EffortDuration from(
-                                    Entry<Resource, EffortDuration> each) {
-                                EffortDuration overload = getOverloadAt(day,
-                                        each.getKey(), each.getValue());
-                                return overload;
-                            }
-                        });
-            }
-
-            private EffortDuration getOverloadAt(PartialDay day,
-                    Resource resource, EffortDuration assignedDuration) {
-                ICalendar calendar = resource.getCalendarOrDefault();
-                EffortDuration workableDuration = calendar
-                        .getCapacityOn(day);
-                if (assignedDuration.compareTo(workableDuration) > 0) {
-                    return assignedDuration.minus(workableDuration);
-                }
-                return zero();
-            }
-        }.calculate(dayAssignmentGrouped.entrySet());
-    }
-
-    private SortedMap<LocalDate, EffortDuration> calculateAvailabilityDurationByDay(
-            final List<Resource> resources, LocalDate start, LocalDate finish) {
-        return new EffortByDayCalculator<Entry<LocalDate, List<Resource>>>() {
-
-            @Override
-            protected LocalDate getDayFor(
-                    Entry<LocalDate, List<Resource>> element) {
-                return element.getKey();
-            }
-
-            @Override
-            protected EffortDuration getDurationFor(
-                    Entry<LocalDate, List<Resource>> element) {
-                LocalDate day = element.getKey();
-                return sumCalendarCapacitiesForDay(resources, day);
-            }
-
-        }.calculate(getResourcesByDateBetween(resources, start, finish));
-    }
-
-    protected static EffortDuration sumCalendarCapacitiesForDay(
+    private static EffortDuration sumCalendarCapacitiesForDay(
             Collection<? extends Resource> resources, LocalDate day) {
 
         final PartialDay wholeDay = PartialDay.wholeDay(day);
@@ -281,13 +238,4 @@ public class ResourceLoadChartData implements ILoadChartData {
         return resource.getCalendarOrDefault().getCapacityOn(day);
     }
 
-    private Set<Entry<LocalDate, List<Resource>>> getResourcesByDateBetween(
-            List<Resource> resources, LocalDate start, LocalDate finish) {
-        Map<LocalDate, List<Resource>> result = new HashMap<LocalDate, List<Resource>>();
-        for (LocalDate date = new LocalDate(start); date.compareTo(finish) <= 0; date = date
-                .plusDays(1)) {
-            result.put(date, resources);
-        }
-        return result.entrySet();
-    }
 }
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/workingday/EffortDuration.java b/navalplanner-business/src/main/java/org/navalplanner/business/workingday/EffortDuration.java
index 987e13089..254aa71e5 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/workingday/EffortDuration.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/workingday/EffortDuration.java
@@ -130,6 +130,16 @@ public class EffortDuration implements Comparable<EffortDuration> {
         return result;
     }
 
+    public static EffortDuration sum(EffortDuration... summands) {
+        return sum(Arrays.asList(summands), new IEffortFrom<EffortDuration>() {
+
+            @Override
+            public EffortDuration from(EffortDuration each) {
+                return each;
+            }
+        });
+    }
+
     public static EffortDuration zero() {
         return elapsing(0, Granularity.SECONDS);
     }