diff --git a/server/budgeting.go b/server/budgeting.go
index 3e6b249..8a77950 100644
--- a/server/budgeting.go
+++ b/server/budgeting.go
@@ -204,10 +204,10 @@ func (*Handler) CalculateCategoryBalances(cat *postgres.GetCategoriesRow,
 		}
 
 		moneyUsed.SubI(bal.Assignments)
-		categoryWithBalance.Available = categoryWithBalance.Available.Add(bal.Assignments)
-		categoryWithBalance.Available = categoryWithBalance.Available.Add(bal.Transactions)
+		categoryWithBalance.Available.AddI(bal.Assignments)
+		categoryWithBalance.Available.AddI(bal.Transactions)
 		if !categoryWithBalance.Available.IsPositive() && bal.Date.Before(firstOfMonth) {
-			moneyUsed.Add(categoryWithBalance.Available)
+			moneyUsed.AddI(categoryWithBalance.Available)
 			categoryWithBalance.Available = numeric.Zero()
 		}