How the calculator works
Each month your balance grows by the monthly interest rate, and then your deposit is added. The rate you enter is a yearly APY, so the monthly rate is the one that adds up to exactly that over twelve months: 4% a year grows a balance by exactly 4% in a year. It counts the months until the balance first reaches your goal. It also answers the opposite question: given the date you want, how much do you need to deposit each month? Both come from the standard formula for a balance that grows with regular deposits.
balance after n months = start × (1 + r)n + deposit × ((1 + r)n − 1) ÷ r
where r = (1 + yearly rate)1/12 − 1. With a 0% rate the formula is just start + deposit × n.
Worked example: $20,000 from $2,000
Someone has $2,000 saved, adds $300 a month, and earns 4% a year. The monthly rate is (1 + 4%)1/12 − 1 = 0.3274%. After 53 months the balance is $19,710, just under the goal, and after 54 months it is $20,075. So the goal is reached in 4 years, 6 months. Of the $20,000, $16,200 is deposits and $1,875 is interest, on top of the $2,000 they began with.
What if they want it in 3 years?
At $300 a month, they would have $13,692 after 36 months, which is $6,308 short. To reach $20,000 in exactly 3 years they would need to deposit about $465 a month. Put that amount back into the calculator, and the balance on the target date equals the goal.
What the interest rate changes
| Account pays | Time to $20,000 | Interest earned |
|---|---|---|
| 0% (cash) | 5 years | $0 |
| 0.37% (FDIC national average for savings) | 5 years | $202 |
| 4% (example) | 4 years, 6 months | $1,875 |
Cash and an account at the national average both take 5 years, so the 4% account saves this saver 6 months. The FDIC publishes that average and updates it regularly. A rate is not guaranteed, and it can change after you open the account, so check what yours pays now.
Ways to reach a goal sooner
- Automate it. Set a transfer for the day after payday, so saving happens before spending.
- Raise the deposit a little. Try adding $50 to the box above and see how many months it removes.
- Keep the money where it earns something. Compare the rate you get with what other accounts pay.
- Add windfalls. A tax refund or bonus put into "saved so far" moves the finish line closer.
- Move the date, not the goal. If the monthly amount looks too high, a later date lowers it.
What this calculator leaves out
- Taxes on interest. The results are before tax.
- Inflation. A goal that is years away may cost more by then.
- Rate changes. It uses one rate for the whole time, though real savings rates move.
- Fees. Some accounts charge fees or require minimum balances.
Saving for something far away, like retirement? The retirement calculator shows whether your plan is on track, and the compound interest calculator shows how growth builds over decades. Carrying debt? Pay attention to the rate: paying off a card that charges 20% usually beats saving at 4%. Try the debt payoff calculator.
Sources and review
The formula is the standard future value of regular deposits, tested against a month-by-month search. The national savings rate of 0.37% is from the FDIC's national rates and rate caps page, as of September 21, 2026. Last reviewed September 2026. Read about our methodology.