Sinking Fund Calculator - Regular Savings Payments

The sinking fund calculator solves for the regular deposit that will grow to a known future amount. Companies originally used sinking funds to retire a bond; households use the same math for a roof replacement, a balloon insurance deductible, a wedding, or a cash down payment. You name the future value, the time, and the rate the cash can earn; the calculator returns the monthly payment. Monthly rate r is the annual rate divided by 12, and n is years times 12. An optional opening deposit is grown to PV × (1+r)^n and subtracted from the target so you only fund the gap. The payment is then gap × r / ((1+r)^n − 1), or gap / n if the rate is zero. Deposits are end-of-month. If the grown opening balance already exceeds the target, the required payment can be zero or negative; a negative figure means you could withdraw and still hit the goal, which is a signal to check inputs. Sinking funds beat “we will figure it out later” because they turn a lumpy expense into a level transfer. A $12,000 roof in three years at 4% is not $12,000 / 36 if the cash earns interest—the payment is a bit lower. If the money sits in a 0% checking account, set the rate to zero and you get a straight divide. Do not use a 10% investment return for a bill that comes due whether markets cooperate or not; a savings or money-market rate is the honest input. Taxes, account fees, and inflation of the future bill are outside the formula. If roof prices rise 5% a year, raise the target rather than the rate. Put the monthly payment on an automatic transfer the same day as payday so the plan does not depend on leftover cash. The sinking fund calculator is an educational payment estimate, not a construction bid, insurance quote, or investment recommendation.