How the calculation works
Your goal is reached by two things: the growth of what you have already saved, and the growth of your regular deposits. The calculator first works out what your starting amount grows to. The deposits have to cover the rest.
i = r / 12
Deposit = (Goal − A × (1 + i)m) × i / ((1 + i)m − 1)
A = amount already saved · r = yearly interest rate as a decimal · i = monthly rate · m = number of months. This is for monthly deposits at the end of each month. With a 0% rate the deposit is (Goal − A) / m.For other deposit schedules the calculator simulates the account step by step. The final balance grows in proportion to the deposit, so the required deposit can be solved exactly.
Worked example
You want 50,000 in 10 years. You have 5,000 already and earn 5% a year, compounded monthly (m = 120).
- Monthly rate: i = 0.05 / 12 = 0.0041667.
- Growth factor: (1 + i)120 = 1.64701.
- Your 5,000 grows to 5,000 × 1.64701 = 8,235.
- The deposits must provide 50,000 − 8,235 = 41,765.
- Deposit: 41,765 × 0.0041667 / (1.64701 − 1) = 268.96 a month.
- You deposit 32,275 in total; the other 12,725 is interest.
How long will it take?
In this mode the calculator adds your deposits and interest month by month and reports the first month in which the balance reaches the goal. With 300 a month in the example above, that is after 9 years and 3 months.
What this calculator does not include
- Tax on interest or investment gains, and account fees.
- Inflation. A fixed target buys less in the future than it does today.
- A rate that changes. Savings rates and investment returns vary over time.
Amounts are rounded for display only; the calculation itself is not rounded. Results are estimates for information, not financial advice. Last updated: 12 November 2026.
Frequently asked questions
What interest rate should I use?
Use the rate your savings account pays, or a cautious estimate of the yearly return if you invest. If you are unsure, try a lower and a higher rate to see how much the answer changes.
What if I cannot afford the deposit shown?
You can extend the time, lower the goal or start with a larger amount. Switch to "How long will it take" to see when you reach the goal with the amount you can save.
Does it matter if I save at the start or the end of the month?
A little. Deposits at the start earn interest for one extra period, so you need a slightly smaller deposit to reach the same goal.
Is inflation included?
No. The goal is in today's money as you entered it. For a goal many years away, consider raising the target to allow for higher prices.
Why is the interest so small for short goals?
Interest needs time to build up. For a goal one or two years away, almost all of the money comes from your own deposits.