ConverterHub

Savings Calculator (with Contributions)

Project savings with monthly deposits and compound interest.

How it is calculated

The tool grows a starting balance and a stream of equal monthly deposits at a fixed annual rate, compounded monthly. The monthly rate is r = rate / 100 / 12 and the number of months is n = years × 12. Then FV = P × (1+r)n + PMT × ((1+r)n − 1) / r, where P is the starting principal, PMT the monthly deposit and rate the nominal annual percentage. Deposits are assumed to be made at the end of each month. If the rate is 0, the formula falls back to P + PMT × n. The second figure shown is the total you paid in: P + PMT × n. Taxes, fees and inflation are not modelled, and the rate is treated as constant for the whole period.

Worked example

Start with 5,000 and add 200 a month for 10 years at 6% a year. Monthly rate: 6 / 100 / 12 = 0.005, and n = 120 months. Growth factor (1.005)120 ≈ 1.8194, so the starting 5,000 grows to about 9,097. The deposits grow by 200 × ((1.8194 − 1) / 0.005) ≈ 32,776. Together that gives a future value of $41,872.85. You contributed 5,000 + 200 × 120 = $29,000.00, so roughly $12,873 of the final balance is interest.

Try this example →

Common mistakes

  • Entering the yearly deposit in the monthly field (or the other way round); the tool multiplies the deposit by 12 times the number of years.
  • Typing the rate as a decimal such as 0.06 instead of 6; the tool expects a percentage.
  • Using an advertised yield that already includes yearly compounding, when this tool compounds the nominal rate monthly, so the result will differ slightly.
  • Expecting the result to be after tax or inflation; neither is deducted, so the real purchasing power will be lower.
  • Entering months in the years field; 18 months must be typed as 1.5.

About this calculator

This calculator combines two effects: compound interest growing the starting principal, and a future value of annuity calculation for a stream of regular monthly deposits added on top — the full formula is FV = P(1+r)ⁿ + PMT × [((1+r)ⁿ − 1)/r]. This is different from a plain compound-interest calculator, which only handles a single lump sum.

It's used by people saving toward retirement, a house down payment, or an emergency fund who plan to contribute a fixed amount every month, letting them see how much of the final balance comes from their own deposits versus investment growth.

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