diff --git a/ana/predictor.go b/ana/predictor.go
index 5e6efb1..f2d4812 100644
--- a/ana/predictor.go
+++ b/ana/predictor.go
@@ -39,10 +39,31 @@ func NewInterestPredictor(namePattern string, currencyPattern string, apy float6
 
 func NewContributionPredictor(reg ledger.Register) Predictor {
 	monthlyRate := getMonthlyContributionRate(reg)
+	_ = monthlyRate
 	return func(given ledger.Balances, delta time.Duration) ledger.Balances {
 		panic(nil)
 	}
 }
 
 func getMonthlyContributionRate(reg ledger.Register) map[string]ledger.Balance {
+	panic(nil)
+}
+
+func getRecentContributions(reg ledger.Register) map[string][]ledger.Balance {
+	return getContributions(reg.Between(time.Now().Add(-1*time.Hour*365/2), time.Now()))
+}
+
+func getContributions(reg ledger.Register) map[string][]ledger.Balance {
+	contributions := make(map[string][]ledger.Balance)
+	for _, date := range reg.Dates() {
+		for name := range reg[date] {
+			contributions[name] = append(contributions[name], maps.Clone(reg[date][name]))
+			if a := contributions[name]; len(a) > 1 {
+				for k := range a[len(a)-2] {
+					a[len(a)-1][k] -= a[len(a)-2][k]
+				}
+			}
+		}
+	}
+	return contributions
 }
diff --git a/ana/predictor_test.go b/ana/predictor_test.go
index 37d51a0..bf8d486 100644
--- a/ana/predictor_test.go
+++ b/ana/predictor_test.go
@@ -41,3 +41,48 @@ func TestNewInterestPredictor(t *testing.T) {
 		})
 	}
 }
+
+func TestGetContributions(t *testing.T) {
+	input := ledger.Register{
+		"2001-01": ledger.Balances{
+			"a": ledger.Balance{"x": 1},
+			"b": ledger.Balance{"z": 1},
+		},
+		"2001-02": ledger.Balances{
+			"a": ledger.Balance{"y": 1},
+		},
+		"2001-03": ledger.Balances{
+			"b": ledger.Balance{"z": 2},
+		},
+	}
+
+	got := getContributions(input)
+	if len(got) != 2 {
+		t.Error(len(got))
+	}
+	if len(got["a"]) != 2 {
+		t.Error(len(got["a"]))
+	} else if len(got["a"][0]) != 1 {
+		t.Error(got["a"])
+	} else if got["a"][0]["x"] != 1 {
+		t.Error(got["a"][0])
+	} else if len(got["a"][1]) != 2 {
+		t.Error(got["a"][1])
+	} else if got["a"][1]["x"] != -1 {
+		t.Error(got["a"][1]["x"])
+	} else if got["a"][1]["y"] != 1 {
+		t.Error(got["a"][1]["y"])
+	}
+
+	if len(got["b"]) != 2 {
+		t.Error(len(got["b"]))
+	} else if len(got["b"][0]) != 1 {
+		t.Error(got["b"])
+	} else if got["b"][0]["z"] != 1 {
+		t.Error(got["b"][0])
+	} else if len(got["b"][1]) != 1 {
+		t.Error(got["b"][1])
+	} else if got["b"][1]["z"] != 1 {
+		t.Error(got["b"][1]["z"])
+	}
+}