diff --git a/ledger/predict.go b/ana/interest.go
similarity index 56%
rename from ledger/predict.go
rename to ana/interest.go
index 0a1291d..8433841 100644
--- a/ledger/predict.go
+++ b/ana/interest.go
@@ -1,15 +1,16 @@
-package ledger
+package ana
 
 import (
-	"fmt"
 	"maps"
 	"math"
 	"regexp"
 	"time"
+
+	"gogs.inhome.blapointe.com/ana-ledger/ledger"
 )
 
-func RegisterWithCompoundingInterestPrediction(reg Register, window time.Duration, pattern string, apy float64) (Register, error) {
-	lastBalances := make(Balances)
+func RegisterWithCompoundingInterestPrediction(reg ledger.Register, window time.Duration, pattern string, apy float64) (ledger.Register, error) {
+	lastBalances := make(ledger.Balances)
 	p := regexp.MustCompile(pattern)
 	for _, d := range reg.Dates() {
 		if t, _ := dateToTime(d); time.Now().Before(t) {
@@ -27,7 +28,7 @@ func RegisterWithCompoundingInterestPrediction(reg Register, window time.Duratio
 	for _, predictionTime := range predictedTimes {
 		k := predictionTime.Format("2006-01")
 		if _, ok := result[k]; !ok {
-			result[k] = make(Balances)
+			result[k] = make(ledger.Balances)
 		}
 		for k2, v2 := range lastBalances {
 			if _, ok := result[k][k2]; !ok {
@@ -36,12 +37,12 @@ func RegisterWithCompoundingInterestPrediction(reg Register, window time.Duratio
 		}
 	}
 
-	addedSoFar := make(Balances)
+	addedSoFar := make(ledger.Balances)
 	for _, predictionTime := range predictedTimes {
 		k := predictionTime.Format("2006-01")
 		for name := range lastBalances {
 			if _, ok := addedSoFar[name]; !ok {
-				addedSoFar[name] = make(Balance)
+				addedSoFar[name] = make(ledger.Balance)
 			}
 			for currency := range result[k][name] {
 				// A = P(1 + r/n)**nt
@@ -57,25 +58,3 @@ func RegisterWithCompoundingInterestPrediction(reg Register, window time.Duratio
 
 	return result, nil
 }
-
-func predictionTimes(window time.Duration) []time.Time {
-	result := []time.Time{}
-	last := time.Now()
-	for last.Before(time.Now().Add(window)) {
-		last = last.Add(-1 * time.Hour * 24 * time.Duration(last.Day())).Add(time.Hour * 24 * 33)
-		result = append(result, last)
-	}
-	return result
-}
-
-func dateToTime(s string) (time.Time, error) {
-	for _, layout := range []string{
-		"2006-01-02",
-		"2006-01",
-	} {
-		if t, err := time.ParseInLocation(layout, s, time.Local); err == nil {
-			return t, err
-		}
-	}
-	return time.Time{}, fmt.Errorf("no layout matching %q", s)
-}
diff --git a/ana/interest_test.go b/ana/interest_test.go
new file mode 100644
index 0000000..26be7a3
--- /dev/null
+++ b/ana/interest_test.go
@@ -0,0 +1,26 @@
+package ana
+
+import (
+	"testing"
+	"time"
+)
+
+func TestInterest(t *testing.T) {
+	input := newTestRegister()
+
+	got, err := RegisterWithCompoundingInterestPrediction(input, time.Hour*24*365, "X", .04)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Logf("%+v", got)
+
+	if len(got) <= len(input) {
+		t.Error(len(got))
+	}
+
+	for _, date := range got.Dates() {
+		for name, balance := range got[date] {
+			t.Logf("%s | %s %s", date, name, balance.Debug())
+		}
+	}
+}
diff --git a/ledger/predict_test.go b/ledger/predict_test.go
deleted file mode 100644
index f92c5d8..0000000
--- a/ledger/predict_test.go
+++ /dev/null
@@ -1,48 +0,0 @@
-package ledger
-
-import (
-	"testing"
-	"time"
-)
-
-func TestRegisterPrediction(t *testing.T) {
-	t.Run("compounding interest", func(t *testing.T) {
-		input := newTestRegister()
-
-		got, err := RegisterWithCompoundingInterestPrediction(input, time.Hour*24*365, "X", .04)
-		if err != nil {
-			t.Fatal(err)
-		}
-		t.Logf("%+v", got)
-
-		if len(got) <= len(input) {
-			t.Error(len(got))
-		}
-
-		for _, date := range got.Dates() {
-			for name, balance := range got[date] {
-				t.Logf("%s | %s %s", date, name, balance.Debug())
-			}
-		}
-	})
-}
-
-func newTestRegister() map[string]Balances {
-	s := func(t time.Time) string {
-		return t.Format("2006-01")
-	}
-	day := time.Hour * 24
-	lastYear := time.Now().Add(-1 * day * time.Duration(time.Now().YearDay()))
-	return map[string]Balances{
-		s(lastYear.Add(day * 0)):   Balances{"X": Balance{USD: 1}},
-		s(lastYear.Add(day * 32)):  Balances{"X": Balance{USD: 2}},
-		s(lastYear.Add(day * 64)):  Balances{"X": Balance{USD: 3}},
-		s(lastYear.Add(day * 94)):  Balances{"X": Balance{USD: 4}},
-		s(lastYear.Add(day * 124)): Balances{"X": Balance{USD: 5}},
-		s(lastYear.Add(day * 154)): Balances{"X": Balance{USD: 6}},
-		s(lastYear.Add(day * 184)): Balances{"X": Balance{USD: 8}},
-		s(lastYear.Add(day * 214)): Balances{"X": Balance{USD: 10}},
-		s(lastYear.Add(day * 244)): Balances{"X": Balance{USD: 12}},
-		s(lastYear.Add(day * 274)): Balances{"X": Balance{USD: 16, "XYZ": 1}},
-	}
-}
diff --git a/ledger/register.go b/ledger/register.go
index c090bc3..f207104 100644
--- a/ledger/register.go
+++ b/ledger/register.go
@@ -1,6 +1,7 @@
 package ledger
 
 import (
+	"fmt"
 	"slices"
 	"time"
 )
@@ -53,8 +54,27 @@ func (register Register) Times() []time.Time {
 	dates := register.Dates()
 	result := make([]time.Time, len(dates))
 	for i := range dates {
-		v, _ := dateToTime(dates[i])
-		result[i] = v
+		result[i] = mustDateToTime(dates[i])
 	}
 	return result
 }
+
+func mustDateToTime(s string) time.Time {
+	result, err := dateToTime(s)
+	if err != nil {
+		panic(err)
+	}
+	return result
+}
+
+func dateToTime(s string) (time.Time, error) {
+	for _, layout := range []string{
+		"2006-01-02",
+		"2006-01",
+	} {
+		if t, err := time.ParseInLocation(layout, s, time.Local); err == nil {
+			return t, err
+		}
+	}
+	return time.Time{}, fmt.Errorf("no layout matching %q", s)
+}