diff --git a/ana/bpi.go b/ana/bpi.go
new file mode 100644
index 0000000..2a7d6fe
--- /dev/null
+++ b/ana/bpi.go
@@ -0,0 +1,42 @@
+package ana
+
+import (
+	"maps"
+	"regexp"
+	"time"
+
+	"gogs.inhome.blapointe.com/ana-ledger/ledger"
+)
+
+func BPIsWithFixedGrowthPrediction(bpis ledger.BPIs, window time.Duration, pattern string, apy float64) (ledger.BPIs, error) {
+	last := map[ledger.Currency]struct {
+		t string
+		v float64
+	}{}
+	for currency, bpi := range bpis {
+		for date, value := range bpi {
+			if date > last[currency].t {
+				was := last[currency]
+				was.t = date
+				was.v = value
+				last[currency] = was
+			}
+		}
+	}
+
+	result := make(ledger.BPIs)
+	p := regexp.MustCompile(pattern)
+	for currency, v := range bpis {
+		result[currency] = maps.Clone(v)
+		if p.MatchString(string(currency)) {
+			for _, predictionTime := range predictionTimes(window) {
+				k2 := predictionTime.Format("2006-01")
+				was := last[currency]
+				was.v *= 1.0 + (apy / 12.0)
+				result[currency][k2] = was.v
+				last[currency] = was
+			}
+		}
+	}
+	return result, nil
+}
diff --git a/ana/bpi_test.go b/ana/bpi_test.go
new file mode 100644
index 0000000..aa754a3
--- /dev/null
+++ b/ana/bpi_test.go
@@ -0,0 +1,35 @@
+package ana
+
+import (
+	"slices"
+	"testing"
+	"time"
+
+	"gogs.inhome.blapointe.com/ana-ledger/ledger"
+)
+
+func TestBPIPrediction(t *testing.T) {
+	t.Run("fixed growth", func(t *testing.T) {
+		bpis := ledger.BPIs{
+			ledger.USD: ledger.BPI{
+				"2001-01": -1000,
+				"2001-02": 100,
+			},
+		}
+
+		got, err := BPIsWithFixedGrowthPrediction(bpis, time.Hour*24*365, string(ledger.USD), 0.06)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		dates := []string{}
+		for d := range got[ledger.USD] {
+			dates = append(dates, d)
+		}
+		slices.Sort(dates)
+
+		for _, d := range dates {
+			t.Logf("%s | %s %.2f", ledger.USD, d, got[ledger.USD][d])
+		}
+	})
+}
diff --git a/ana/window.go b/ana/window.go
new file mode 100644
index 0000000..4ef1b9c
--- /dev/null
+++ b/ana/window.go
@@ -0,0 +1,13 @@
+package ana
+
+import "time"
+
+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
+}
diff --git a/ledger/predict.go b/ledger/predict.go
index 5810c12..5635f7c 100644
--- a/ledger/predict.go
+++ b/ledger/predict.go
@@ -124,39 +124,6 @@ func registerWithContributionPredictionForNameForCurrency(reg Register, window t
 	return nil
 }
 
-func BPIsWithFixedGrowthPrediction(bpis BPIs, window time.Duration, pattern string, apy float64) (BPIs, error) {
-	last := map[Currency]struct {
-		t string
-		v float64
-	}{}
-	for currency, bpi := range bpis {
-		for date, value := range bpi {
-			if date > last[currency].t {
-				was := last[currency]
-				was.t = date
-				was.v = value
-				last[currency] = was
-			}
-		}
-	}
-
-	result := make(BPIs)
-	p := regexp.MustCompile(pattern)
-	for currency, v := range bpis {
-		result[currency] = maps.Clone(v)
-		if p.MatchString(string(currency)) {
-			for _, predictionTime := range predictionTimes(window) {
-				k2 := predictionTime.Format("2006-01")
-				was := last[currency]
-				was.v *= 1.0 + (apy / 12.0)
-				result[currency][k2] = was.v
-				last[currency] = was
-			}
-		}
-	}
-	return result, nil
-}
-
 func RegisterWithCompoundingInterestPrediction(reg Register, window time.Duration, pattern string, apy float64) (Register, error) {
 	lastBalances := make(Balances)
 	p := regexp.MustCompile(pattern)
diff --git a/ledger/predict_test.go b/ledger/predict_test.go
index fbb8dda..39c7720 100644
--- a/ledger/predict_test.go
+++ b/ledger/predict_test.go
@@ -1,7 +1,6 @@
 package ledger
 
 import (
-	"slices"
 	"testing"
 	"time"
 )
@@ -51,32 +50,6 @@ func TestRegisterPrediction(t *testing.T) {
 	})
 }
 
-func TestBPIPrediction(t *testing.T) {
-	t.Run("fixed growth", func(t *testing.T) {
-		bpis := BPIs{
-			USD: BPI{
-				"2001-01": -1000,
-				"2001-02": 100,
-			},
-		}
-
-		got, err := BPIsWithFixedGrowthPrediction(bpis, time.Hour*24*365, string(USD), 0.06)
-		if err != nil {
-			t.Fatal(err)
-		}
-
-		dates := []string{}
-		for d := range got[USD] {
-			dates = append(dates, d)
-		}
-		slices.Sort(dates)
-
-		for _, d := range dates {
-			t.Logf("%s | %s %.2f", USD, d, got[USD][d])
-		}
-	})
-}
-
 func newTestRegister() map[string]Balances {
 	s := func(t time.Time) string {
 		return t.Format("2006-01")