Rex says
Money math without the spreadsheet headache. Plug in your numbers and I'll show you exactly where the dollars land.
Try a scenario
Click to load — tweak from there.Inputs
Result
Monthly contribution needed
$293
Equivalent weekly amount
$68
Cost at the due date
$6,272
Gap left to fund
$5,423
Total you'll contribute
$5,271
Interest doing the rest
$201
Psst — share this and help Rex grow
One click, a permanent link with your numbers baked in.
Got your number — what next?
Pick one, it takes 20 secondsHow to use this
- 1Enter amount you'll need ($).
- 2Enter months until it's due (months).
- 3Enter already saved ($).
- 4Enter savings apy (%).
- 5Enter annual cost inflation on the item (%).
- 6Read your monthly contribution needed on the right — it updates as you type.
- 7Hit Share to keep the scenario or send it to someone.
About this calculator
A sinking fund is a savings account with a job: a known expense at a known date, funded in advance in equal instalments. Property tax bills, insurance renewals, a car replacement, a roof, a wedding — all of them are predictable, and all of them end up on a credit card when they are not pre-funded. This calculator takes the target amount, the date it is due, what you have already saved, and the interest your savings earn, and returns the exact monthly contribution required. Fund the largest, nearest item first; a fund that is short at the deadline still cost you the discipline without the benefit.
Worked example
Using the values the calculator loads with:
Inputs
- Amount you'll need: 6000 $
- Months until it's due: 18 months
- Already saved: 800 $
- Savings APY: 4 %
- Annual cost inflation on the item: 3 %
Results
- Monthly contribution needed: $292.81
- Equivalent weekly amount: $67.57
- Cost at the due date: $6,272.01
- Gap left to fund: $5,422.63
- Total you'll contribute: $5,270.61
- Interest doing the rest: $201.41
What each field means
Inputs
- Amount you'll need ($)
- The amount you'll need used in the calculation, measured in $. Starts at 6000 $ so you have a working example on load.
- Months until it's due (months)
- The months until it's due used in the calculation, measured in months. Starts at 18 months so you have a working example on load.
- Already saved ($)
- The already saved used in the calculation, measured in $. Starts at 800 $ so you have a working example on load.
- Savings APY (%)
- The savings apy used in the calculation, measured in %. Starts at 4 % so you have a working example on load.
- Annual cost inflation on the item (%)
- The annual cost inflation on the item used in the calculation, measured in %. Starts at 3 % so you have a working example on load.
Results
- Monthly contribution needed
- Returned as a money amount in US dollars and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Equivalent weekly amount
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Cost at the due date
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Gap left to fund
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Total you'll contribute
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Interest doing the rest
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How is this different from an emergency fund?
An emergency fund covers unknown events and should not be spent on scheduled ones. A sinking fund covers a known expense with a date. Keeping them in separate accounts is what stops a predictable car registration bill from quietly draining the buffer meant for job loss.
Where should the money sit?
Somewhere liquid and insured — a high-yield savings account or money market fund. For horizons beyond a couple of years, a short-dated CD or T-bill ladder maturing near the due date can add yield without meaningful risk. Do not invest sinking funds in equities; the date is fixed and the market's is not.
Should I run several funds at once?
Yes, and most people do — sub-accounts or labelled buckets for insurance, car, home, travel. Total them and compare against your monthly surplus; if the sum exceeds what you have, extend the timelines or reduce the targets rather than underfunding everything equally.
Why include inflation on the item?
Because the target you priced today is not what you will pay in two years, especially for construction, insurance premiums, and vehicles. Growing the target keeps the fund from landing short at exactly the moment you need it whole.
Accuracy and limitations
- Results are estimates before tax, fees, and inflation unless an input explicitly covers them.
- Rates are treated as fixed for the whole period — variable-rate products will drift from this projection.
- This is educational maths, not financial advice. Check anything contractual with the lender or your accountant.
Related tools
Emergency Fund Target Calculator
Size your cash buffer against real essential spending and your income stability.
Savings Goal Date Calculator
Find the month you hit a savings target at your current contribution and rate.
Car Buy vs Lease Cost Calculator
Compare the true cost per month of financing a car against leasing the same vehicle.
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Sinking Fund Monthly Contribution Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/sinking-fund-monthly
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/sinking-fund-monthly" target="_blank" rel="noopener">Sinking Fund Monthly Contribution Calculator — RevenueLab</a> (2026).</p>
Source: [Sinking Fund Monthly Contribution Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/sinking-fund-monthly) (2026).