Savings Goal Calculator

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.

Common mistakes

1. Using a stock-market return assumption for a short-term goal. For goals under a few years, market swings can leave the balance below where it started right when the money is needed — use the actual APY of a deposit account instead.
2. Skipping early deposits and hoping to catch up later. The monthly figure assumes consistent deposits from the start — missing early months means later ones must be larger to hit the same deadline.
3. Forgetting to revisit the plan as the rate changes. Savings account APYs move with the broader rate environment; a rate drop raises the required deposit slightly, and a better competing rate effectively deposits money for free.
4. Treating a $0 required deposit as a data error. If current savings will compound past the goal alone, that’s the calculator working correctly — it’s a signal to redirect the money you’d budgeted, not a bug.

Practical tips

1. 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.
2. 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.
3. 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.
4. 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.