diff --git a/ana/predictor.go b/ana/predictor.go
index 5f66e71..5e6efb1 100644
--- a/ana/predictor.go
+++ b/ana/predictor.go
@@ -36,3 +36,13 @@ func NewInterestPredictor(namePattern string, currencyPattern string, apy float6
 		return result
 	}
 }
+
+func NewContributionPredictor(reg ledger.Register) Predictor {
+	monthlyRate := getMonthlyContributionRate(reg)
+	return func(given ledger.Balances, delta time.Duration) ledger.Balances {
+		panic(nil)
+	}
+}
+
+func getMonthlyContributionRate(reg ledger.Register) map[string]ledger.Balance {
+}
diff --git a/ledger/register.go b/ledger/register.go
index f207104..9dc66c0 100644
--- a/ledger/register.go
+++ b/ledger/register.go
@@ -2,6 +2,7 @@ package ledger
 
 import (
 	"fmt"
+	"maps"
 	"slices"
 	"time"
 )
@@ -50,6 +51,18 @@ func (register Register) Dates() []string {
 	return result
 }
 
+func (register Register) Between(start, end time.Time) Register {
+	result := make(Register)
+	for k := range register {
+		t := mustDateToTime(k)
+		if t.Before(start) || t.After(end) {
+			continue
+		}
+		result[k] = maps.Clone(register[k])
+	}
+	return result
+}
+
 func (register Register) Times() []time.Time {
 	dates := register.Dates()
 	result := make([]time.Time, len(dates))
diff --git a/ledger/register_test.go b/ledger/register_test.go
new file mode 100644
index 0000000..455a2c6
--- /dev/null
+++ b/ledger/register_test.go
@@ -0,0 +1,31 @@
+package ledger
+
+import (
+	"testing"
+	"time"
+)
+
+func TestRegisterBetween(t *testing.T) {
+	reg := make(Register)
+	reg["2001-01"] = make(Balances)
+	reg["2002-01"] = make(Balances)
+	reg["2003-01"] = make(Balances)
+	reg["2004-01"] = make(Balances)
+	reg["2005-01"] = make(Balances)
+
+	start, _ := time.ParseInLocation("2006-01", "2002-01", time.Local)
+	end, _ := time.ParseInLocation("2006-01", "2004-01", time.Local)
+	got := reg.Between(start, end)
+	if len(got) != 3 {
+		t.Error(len(got))
+	}
+	if _, ok := got["2002-01"]; !ok {
+		t.Error("2002-01")
+	}
+	if _, ok := got["2003-01"]; !ok {
+		t.Error("2003-01")
+	}
+	if _, ok := got["2004-01"]; !ok {
+		t.Error("2004-01")
+	}
+}