Find the monthly deposit that reaches a goal in a set time, or how long a set deposit takes.
Work out Monthly deposit when you know when you want the money: type the goal, the amount saved so far, the yearly return and the time. Work out Time needed when you know what you can set aside each month: type the deposit instead of the time. The page opens on a goal of 10,000 with 1,000 saved, a 5% yearly return and 3 years, which needs 228.07 a month. Time can be given in years or months and must make a whole number of months, from 1 month to 100 years, so 2.5 years is accepted and 2.55 is not. The goal must be more than 0, saved so far can be 0, and the return can be 0 to 100.
Interest compounds monthly at the yearly return divided by 12, and each deposit is made at the end of its month, so it earns interest from the next month. The balance after n months is saved × (1 + r)^n + deposit × ((1 + r)^n − 1) ÷ r, where r is the monthly rate. For a 10,000 goal with nothing saved, 6% and 5 years, r is 0.005, n is 60 and the deposit is 143.33. At a 0% return the formula would divide by zero, so the page uses the plain version: (goal − saved) ÷ months, which is 166.67 for the same goal and time. The box under the answer repeats each step with your numbers.
In Time needed mode the page estimates the number of months with a logarithm, then checks the months just before and after the estimate and picks the first whole month where the balance reaches the goal, so the answer is always a whole number of months. A deposit of 100 a month at 12% a year reaches 1,000 after 10 months, when the balance is 1,046.22. If the amount saved already equals or exceeds the goal the answer is 0 months. A deposit of 0 can still work when the saved amount grows to the goal on its own, for example 1,000 at 12% reaching 2,000 in 5 years 10 months. If the goal is not reached within 100 years, the page says so and shows no result.
The return is an assumption you type, not a prediction, and real returns vary. The page does not model fees, taxes, inflation or a deposit that changes over time. The monthly deposit is shown rounded to cents, so paying exactly the shown amount can leave the final balance a few cents away from the goal. The table lists deposits, interest and balance for each year, and a last partial year when the time is not a whole number of years. Amounts have no currency symbol and are rounded to 2 decimals only when shown. This is an estimate, not financial advice.
With nothing saved and a 0% return, 10,000 ÷ 60 months = 166.67 a month. At a 6% yearly return, compounded monthly with deposits at the end of each month, it is 143.33 a month. Set Work out to Monthly deposit and type the goal, the return and 5 years.
Choose Time needed and type the deposit. With 100 a month, 0 saved and a 0% return, 1,000 takes 10 months. At 12% a year it also takes 10 months, because the balance after 10 months is 1,046.22 and after 9 months it is 936.85.
Yes. A return of 0 is allowed and means no growth: the deposit is (goal − saved) ÷ months, and the time is (goal − saved) ÷ deposit rounded up to a whole month. Interest earned shows 0.00.
At the end. A deposit made in month 1 earns interest from month 2, and the last deposit earns none. A start-of-month schedule would give a slightly smaller required deposit. The sip-calculator uses start-of-month deposits.
The goal is not reached within 100 years (1,200 months) with those numbers. For example, a deposit of 0 with nothing saved never reaches a goal. Raise the deposit, lower the goal or raise the return.