diff --git a/ledger/predict.go b/ledger/predict.go
index 3b0aa77..3db8ade 100644
--- a/ledger/predict.go
+++ b/ledger/predict.go
@@ -185,16 +185,21 @@ func RegisterWithCompoundingInterestPrediction(reg Register, window time.Duratio
 		}
 	}
 
+	addedSoFar := make(Balances)
 	for _, predictionTime := range predictedTimes {
 		k := predictionTime.Format("2006-01")
 		for name := range lastBalances {
+			if _, ok := addedSoFar[name]; !ok {
+				addedSoFar[name] = make(Balance)
+			}
 			for currency := range result[k][name] {
 				// A = P(1 + r/n)**nt
-				p := result[k][name][currency]
+				p := result[k][name][currency] + addedSoFar[name][currency]
 				r := apy
 				n := 12.0
-				t := float64(predictionTime.Sub(time.Now()) / (time.Hour * 24 * 365))
+				t := 1.0 / 12.0
 				result[k][name][currency] = p * math.Pow(1.0+(r/n), n*t)
+				addedSoFar[name][currency] += (result[k][name][currency] - p)
 			}
 		}
 	}