Savings Goal Calculator — Monthly Amount Needed

What this calculator does

Most savings calculators answer “what will I have?” This one answers the more actionable question: “what do I have to do?” Give it the goal, what you’ve saved so far, your account’s interest rate, and the deadline — it returns the exact monthly deposit that gets you there, plus how much of the goal your deposits cover versus how much interest contributes.

It also recognizes when you’re already done: if your current balance will grow past the goal on its own, the answer is $0, and it says so.

How the math works

Your future balance has two parts — the current savings growing at compound interest, and the stream of monthly deposits (an annuity):

Goal = P₀(1 + i)ⁿ + PMT · ((1 + i)ⁿ − 1) / i

where P₀ is today’s balance, i the monthly rate (APY ÷ 12), n the months, and PMT the deposit we’re solving for. Rearranged:

PMT = (Goal − P₀(1 + i)ⁿ) · i / ((1 + i)ⁿ − 1)

With no interest the formula collapses to simple division: (goal − savings) ÷ months.

A worked example

Goal: $20,000 for a house down payment in 36 months, starting from $5,000, in a high-yield account earning 4% APY:

Monthly rate: 4% ÷ 12 = 0.3333%
Your $5,000 grows on its own to about $5,636 by month 36
Remaining gap: $14,364, filled by deposits earning interest as they accumulate
Required deposit: $376.19 per month

Total deposits come to about $13,543; interest contributes roughly $1,457. Without the 4% account, the same goal needs $416.67 a month — the interest is effectively paying one of your three years’ worth of coffee budgets.

Practical tips

Name the account after the goal. Most banks let you nickname savings accounts (“House 2029”). Money with a label is measurably harder to raid — the CFPB’s Start Small, Save Up materials lean on exactly this behavioral effect.
Automate on payday, not month-end. A transfer that happens before you can spend the money succeeds; one that waits for leftovers doesn’t. The formula assumes consistency — automation provides it.
Revisit the rate twice a year. High-yield savings rates move with the Federal Reserve. A rate drop from 4% to 3% on this example adds about $10 to the required monthly deposit — trivial — but a competitor paying 1% more effectively deposits money for you.
Split big goals into checkpoints. $20,000 in 36 months is abstract; “$6,700 by this time next year” is checkable. Rerun the calculator annually with your actual balance — if you’re ahead, the required deposit falls, which is the most motivating number in personal finance.

When the answer is “you’re already there”

If your current savings alone will compound past the goal by the deadline, the calculator reports a $0 monthly deposit. That’s not an error — it’s the signal to either upgrade the goal, shorten the timeline, or redirect the monthly amount you were prepared to save toward the next objective. The compound interest calculator shows what that same monthly habit would build over a longer horizon.

Frequently asked questions

Why is the required deposit lower when I enter an interest rate?

Because interest does part of the saving for you. In the worked example on this page, reaching $20,000 in three years takes $376 a month at 4% APY but about $417 with no interest — the account contributes roughly $1,460 of the goal. The longer the timeline, the bigger interest's share.

What interest rate should I use?

Use the APY your money will actually earn. For short-term goals that belong in a high-yield savings account, use that account's published APY (the FDIC tracks national averages, linked below). Avoid using stock-market return assumptions for goals under about five years — market swings can easily leave a short-term balance below where it started.

What if I can't afford the monthly amount shown?

You have three levers: extend the timeline, reduce the goal, or raise the starting amount. Even small timeline changes matter — the required deposit falls roughly in proportion to added months. Rerun the calculator with a longer horizon and see what becomes sustainable; a plan you keep beats an ambitious one you abandon.

Should this money be invested in stocks for the higher return?

For goals within a few years — a car, a wedding, a house down payment — most planners recommend deposit accounts or short-term Treasuries, because the arrival date is fixed but market returns are not. For flexible goals five or more years out, investing becomes more reasonable. Match the vehicle to the deadline, not to the highest number.

Does the calculator assume deposits at the start or end of each month?

End of month, the standard annuity convention. If you deposit on the 1st instead, you'll finish very slightly ahead of the projection — a pleasant rounding error in your favor.