Savings Goal

This calculator runs the annuity formula backwards. Instead of asking what a given monthly deposit grows into, it asks the question people actually have: what deposit lands me on a fixed number by a fixed date? Goal, current balance, rate and a month count go in; a required monthly deposit comes out.

On a three-year horizon that inversion matters because interest does almost none of the work. At the tool's defaults — a $10,000 goal, $1,000 already saved, 4.5% and 36 months — the required deposit is $230.22, and interest supplies $712 of the $10,000. Nudging the rate barely moves that. Nudging the deadline moves it a lot.

Everything is computed in your browser. Nothing here is financial advice, and a deposit account is not the right container for every goal — see the caveats below.

What the four output fields mean

• Monthly Contribution Needed — a level deposit made at the end of each month.
• Total Contributions — that deposit multiplied by the month count. It does not include your opening balance.
• Interest Earned — computed as goal minus current savings minus total contributions. It is a residual, so it captures every dollar you did not deposit yourself, including growth on the opening balance.
• Goal — an echo of your target, so the panel reads as a complete statement.

One edge case is worth knowing. If your opening balance alone compounds past the goal within the time you set, the required deposit comes back negative. That is not an instruction to withdraw money; it means you are already there and the shortfall the formula is solving for does not exist.

Solving the annuity formula for the deposit

The future value of a level end-of-month deposit is FV = D x ((1 + r)^n - 1) / r. Rearranged for the deposit:

D = Need x r / ((1 + r)^n - 1), where Need = Goal - Current x (1 + r)^n

r is the annual rate divided by 12 and by 100; n is the month count. At a zero rate the whole thing collapses to Need / n.

Because r is the annual figure divided by twelve, the rate box wants a nominal annual rate, not an APY. A bank advertising 4.50% APY is already compounding to that figure; the nominal rate that produces it monthly is about 4.41%. On this goal the distinction is worth under $0.50 a month — but the same confusion carried into a thirty-year projection is not trivial, which is why it is worth naming here.

The default goal, step by step

$10,000 target, $1,000 already saved, 4.5% annual, 36 months:

• Monthly rate: 0.045 / 12 = 0.00375
• Growth factor: (1.00375)^36 = 1.144248
• Future value of the existing $1,000: $1,144.25
• Shortfall the deposits must cover: $10,000 - $1,144.25 = $8,855.75
• Required deposit: $8,855.75 x 0.00375 / 0.144248 = $230.22
• Total deposited: $8,288.00. Interest earned: $712.00 — 7.1% of the goal.

Now change one input. Extend the deadline from 36 months to 48 and the required deposit falls to $167.73, a cut of $62.49 a month. Twelve extra months bought a 27% reduction in what you have to find each month. No rate available on an insured deposit account comes close to that.

Rate versus deadline on a three-year goal

$10,000 in 36 months, starting from nothing:

The full column spans $27 a month, and the top row is a rate you cannot get on money you might need in three years. Now hold the rate at 4.5% and move the deadline instead: 24 months needs $398.98, 36 months needs $259.97, 48 needs $190.53, 60 needs $148.93.

Two extra years is worth $111 a month. A 6.5-point rate swing is worth $27. On a savings goal this short, the calendar is the rate.

Where this model diverges from a real savings account

The rate is treated as fixed for the whole term. Deposit rates are not contractual and they track the policy rate: typical online savings yields moved from well under 1% to above 4% between 2021 and 2023, and they come back down the same way. Re-run the number when your bank changes its rate, not once a year.

Deposits are assumed to land at the end of each month. Depositing on the 1st instead earns one extra month of interest across the term, which lowers the required deposit here from $230.22 to $229.36 — small, but it is the difference between an ordinary annuity and an annuity due, and a bank's own calculator may use the other convention.

Interest is taxable. Deposit-account interest is ordinary income, reported on Form 1099-INT. At a 22% marginal rate the $712 of interest in the worked example is about $556 after federal tax, so the goal is reached slightly later than the arithmetic here suggests. Federal brackets: Tax Estimator.

FDIC deposit insurance covers $250,000 per depositor, per insured bank, per ownership category. Balances beyond that need to be split across institutions. None of this is financial advice.

Where a dated savings goal calculator earns its keep

It fits any target that has both a number and a date attached: a down payment, an emergency fund sized at three to six months of expenses, a wedding, an insurance deductible you want funded before renewal, a tax bill you already know is coming.

It is also usable in reverse as an affordability check. Enter the deposit you can genuinely make, then move the month count until the goal appears. That tells you the earliest honest date rather than the date you hoped for.

It assumes a deposit account. Money needed on a fixed date inside about five years should not sit in something that can be down 20% on that date; the 7% row in the table above is there to show the size of the temptation, not to endorse it. For money with no deadline, Compound Interest projects forward from a rate, and Retirement adds inflation over a working life.

Frequently asked questions

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