Sinking Fund Calculator
Work out the monthly amount you need to save, with compound growth, to hit a future savings target by a set number of months from now.
Monthly contribution needed
$353.18
To reach $10,000.00 in 24 months
Total you'll contribute
$9,476.22
Growth from interest
$523.78
Starting balance
$1,000.00
Assumes you contribute the same amount at the end of every month and the annual return compounds monthly at a constant rate — real accounts rarely grow in a perfectly straight line, so treat this as a planning estimate, not a guarantee. A 0% return simply divides the remaining amount evenly across the months.
About this tool
How to use it
- Enter the amount you're saving toward and how much you've already put aside.
- Enter how many months you have to reach it, and the annual return rate you expect on the savings (use 0% for a plain savings account with no growth assumption).
- Press Calculate Monthly Saving, or just keep typing — the result updates live.
- Check the breakdown below the headline figure to see how much of the total comes from your own contributions versus compound growth.
Why it matters
A 'sinking fund' is money set aside gradually and specifically for a known future expense — a holiday, a deposit, a big purchase, a tax bill — rather than left to chance. Knowing the exact monthly amount needed turns a vague goal ('save up for it') into a concrete, trackable plan, and factoring in compound growth (even a small one, in an interest-bearing account) shows how much less you actually need to contribute yourself compared to simple division.
When to use it
Useful when planning for a known future expense with a target date, when comparing how a higher expected return changes the monthly amount needed, or when checking how much your existing savings already cover before you add anything more.
Good to know
This assumes a level contribution made at the end of every month and a constant annual return that compounds monthly — real savings and investment accounts don't grow in a perfectly straight line, so treat the result as a planning estimate rather than a guarantee, especially at higher return rates or over longer time horizons. Setting the return to 0% simply divides the amount still needed evenly across the remaining months, with no growth assumption at all.
Common questions
What is a sinking fund?
A sinking fund is money set aside gradually and specifically for a known future expense, rather than mixed in with general savings. This calculator works out the level monthly contribution needed to reach a target amount by a set number of months from now.
What if my current savings already cover the target?
The calculator shows $0 as the monthly contribution needed rather than a negative number — if your starting balance, grown at the entered return rate, already reaches or exceeds the target, there's nothing more you need to add.
Why does a higher return rate lower the monthly amount needed?
Compound growth does part of the work for you — the higher the assumed annual return, the more your existing and contributed money grows on its own between now and the target date, so a smaller monthly contribution is needed to make up the difference.
Is the return rate guaranteed?
No — it's an assumption you enter, not a promise. Real interest rates and investment returns fluctuate, so a rate that looks achievable today isn't locked in for the whole savings period. Treat the result as a planning estimate, and revisit it if your actual returns turn out different.
Does this account for taxes or fees on the interest earned?
No — the annual return you enter is treated as the actual net rate your balance grows at. If your account is taxed or charges fees, enter your expected after-tax, after-fee rate rather than the account's stated headline rate for a more realistic result.