What interest rate should I assume for a savings goal?

For a goal within five years, use the rate on a savings account or term deposit you can actually get today, not a hoped-for investment return. Money you need on a fixed date should not be exposed to markets that might be down when the date arrives. For longer horizons a higher assumption becomes more defensible.

Why is the required monthly amount lower than the goal divided by the months?

Because interest is doing part of the work. Your existing balance grows on its own, and every deposit earns a return for the remaining months. The longer the timeframe and the higher the rate, the larger the share that interest contributes and the less you have to find yourself.

What if I already have more than enough saved?

Then the required monthly amount is zero and the calculator says so. If your existing balance will grow past the target on its own before the deadline, no further contributions are needed to get there.

Does this assume I save at the start or the end of each month?

The end of each month, which is the conservative assumption. Saving at the start of the month earns one extra month of interest on every deposit, so you would need very slightly less than the figure shown.

How do I account for inflation on a long-term goal?

If the goal is a real purchase several years away, its price will have risen by then. Either increase the target to the expected future cost, or subtract expected inflation from the interest rate to work in today’s money. Doing neither will leave you short.

Savings Goal Calculator: Monthly Amount Needed

How to use this calculator

Enter your savings goal — the amount you need.
Enter what you have already saved, if anything.
Enter the interest rate you can realistically get, and how long you have.

The result is the amount to transfer each month. The breakdown shows how much of the goal you fund yourself and how much interest covers.

How the calculation works

This is the future-value-of-an-annuity formula rearranged to solve for the payment:

PMT = (FV − PV(1+i)^n) × i / ((1+i)^n − 1)

FV — the goal
PV — what you already have
i — the monthly interest rate
n — the number of months

The logic runs in two steps. First, work out what your existing balance will grow to on its own by the deadline. Whatever is still missing after that is the shortfall your monthly deposits have to cover — and because those deposits also earn interest, you need less than the shortfall divided by the number of months.

A worked example

A $30,000 goal in 5 years, with $5,000 already saved, earning 4%.

Your existing $5,000 compounds for 60 months at 4% ÷ 12:

5000 × (1 + 0.003333)^60 = 6,104.98

That leaves a shortfall of $30,000 − $6,104.98 = $23,895.02 for your deposits to cover.

PMT = 23895.02 × 0.003333 / (1.003333^60 − 1)
PMT = 79.65 / 0.220997
PMT = 360.41

So you need $360.41 a month.


Monthly deposit	$360.41
Total you contribute	$26,624.78
Interest does the rest	$3,375.22
Final balance	$30,000.00

Note what happens without interest: you would need $25,000 ÷ 60 = $416.67 a month. The 4 percent return saves you $56 a month, and interest supplies over 11 percent of the goal.

What rate should you actually assume?

This is the judgement that most affects the answer, and the honest guidance depends entirely on the timeframe.

Under five years, use the rate on a savings account or term deposit you can open today. Money needed on a fixed date should not be sitting in something that might be down 30 percent when the date arrives. A house deposit is the classic example: the downside of missing the target badly outweighs the upside of a slightly better return.

Over ten years, a higher assumption becomes more defensible, because there is time to recover from a bad stretch. Even then, be conservative — it is far better to overshoot the goal than to discover at the deadline that the market disagreed with your projection.

Common mistakes to avoid

Forgetting that the goal itself will cost more later. If you are saving for something whose price rises with inflation — a car, a wedding, a house deposit — the target you set today will be too low by the time you get there. Either inflate the goal or subtract expected inflation from the interest rate. Doing neither leaves you systematically short.

Saving before clearing expensive debt. Paying off a credit card charging 20 percent is a guaranteed 20 percent return, which no savings account will match. The sensible exception is a small emergency fund first, so that an unexpected bill does not put you straight back onto the card you just cleared.

Setting a goal without automating the transfer. The calculation is the easy part. A standing order timed for the day after payday is what actually makes it happen; relying on whatever happens to be left at the end of the month reliably does not.

Ignoring what happens if you start late. Delay is expensive in a way that feels unfair. Cut the timeframe on the example above from five years to three and the required deposit jumps from $360 to $647 — nearly double, for the same goal.

When this calculator is not the right tool

If you want to know what a fixed monthly amount becomes rather than what you need to save, the compound interest calculator answers that question directly. If you are working out whether an investment you already hold has performed well, use the ROI calculator. And for a goal funded by a lump sum rather than monthly deposits, compound interest with a zero contribution is the simpler model.

Savings Goal Calculator