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Sinking-Fund Contribution for a Savings Target

Find a regular end-of-period contribution from a target amount, nominal annual rate, compounding frequency and duration.

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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Use the result with context

Results are estimates for planning and education. Confirm rates, taxes, fees, and legal requirements with the relevant institution or a qualified professional before making a financial decision.

Formula and method

To reach 2,400 in two years with monthly deposits and zero interest, contribute 100 at the end of each month.

Contribution = target × i/[(1+i)^N − 1]; at zero rate, contribution = target/N

Worked example

Enter these known values and leave the other values blank.

Target future amount
2400 USD
Nominal annual interest rate (%)
0 %
Matching deposit and compounding frequency
Monthly
Period
2:0 yrs / mos
Sinking-fund factor
0.04167
Contribution at the end of each period
100 USD

Assumptions and limitations

  • Deposits occur at the end of each compounding period, starting from a zero balance. Deposit and compounding frequencies match.
  • The nominal annual rate is constant and nonnegative. Fees, taxes and missed contributions are excluded.
  • Duration is positive. For a real payment schedule, choose a whole number of deposit periods; fractional periods use the formula’s mathematical extension.
  • The result is an unrounded mathematical contribution. Round according to the account’s currency rules and verify that the rounded schedule reaches the target.

Common questions

What happens at zero interest?

The target is divided equally among the deposit periods; no small substitute interest rate is needed.

Can I use this for deposits at the start of each period?

This model assumes end-of-period deposits. Beginning-of-period deposits earn additional interest and use a different factor.

References

Bookify permits zero interest and requires a nonnegative rate and a positive sinking-fund factor. Bookify evaluates the zero-interest limit directly, including available reverse calculations; nonzero-rate source expressions are preserved.

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