Savings goal calculator

Pick the figure you want and this tool finds it: enter any four of a savings plan's five numbers — starting amount, monthly contribution, interest rate, duration and target — and it works out the fifth. So one calculator answers 'what will I end up with?', 'how much must I save?' and 'how long will it take?'. Every figure is yours to change, and the maths runs in your browser; nothing is stored or sent.

This calculator needs JavaScript because the calculation runs entirely in your browser – so your inputs never leave your device. Two fully worked examples are shown further down this page.

What your result means

The headline figure is whichever value you asked for — a final balance, a monthly contribution, a duration, a starting amount or a rate. Below it, three cards break the plan down: the final balance, total contributions (everything you pay in) and total interest (the balance minus what you put in).

The further apart contributions and interest sit, the more the compounding has done — which grows with a longer term and a higher rate. The year-by-year table shows how the balance builds up.

In 'duration' mode the table is rounded up to whole months, so the final balance sits just above the target.

How this calculator works

The calculator works in monthly periods. The nominal monthly rate is the annual rate divided by twelve. Your starting amount earns interest across the whole term, and each monthly contribution is added either at the start of the month, so it earns that month's interest, or at the end, depending on the timing you choose.

The final balance, the monthly contribution and the starting amount each follow a closed savings-plan formula. The required interest rate and — when the rate is above zero — the duration have no closed solution, so the tool finds them by bisection: it narrows an interval until the result sits within a documented tolerance, with a fixed cap on the number of steps.

In 'duration' mode the time to the goal rarely lands on whole months, so the year-by-year table rounds up to the next whole month and the target is reached a fraction over. Internally the calculation is unrounded and only rounded to the nearest penny for display.

Formula and variables

F = P·q^m + C · (q^m − 1)/(q − 1) · f with q = 1 + i/12, m = 12·nf = 1 (contribution at month end) or f = q (at month start)Contribution: C = (F − P·q^m) / [ (q^m − 1)/(q − 1) · f ]Rate and duration: solved numerically (bisection) from the same equation

F: Final balance or target amount
P: Starting amount (principal)
C: Monthly contribution
i: Annual interest rate as a decimal (4% is 0.04)
n: Duration in years
m: Number of months (12 × n)
q: Monthly factor 1 + i/12
f: Contribution factor: 1 at month end, q at month start

Worked examples

Example 1: the final balance of a plan

Example inputs
Calculating	Final balance
Starting amount	€3,000.00
Monthly contribution (end of month)	€250.00
Interest rate (example assumption)	4% p.a.
Duration	12 years

Example results
Final balance	€50,953.22
Total contributions	€39,000.00
Total interest	€11,953.22

The €3,000.00 starting amount grows month by month, and the 144 contributions of €250.00 grow through the savings-plan formula. Of the €50,953.22 final balance, €39,000.00 is your own money (€3,000.00 plus 144 × €250.00) and €11,953.22 is interest. The 4% rate is an example assumption, not a current market rate.

Example 2: the monthly amount needed for a goal

Example inputs
Calculating	Monthly contribution
Starting amount	€5,000.00
Target	€30,000.00
Interest rate (example assumption)	3.5% p.a.
Duration	8 years

Example results
Required monthly contribution	€211.45
Total contributions	€25,299.32
Total interest	€4,700.68

The tool rearranges the savings-plan formula for the contribution: whatever of the €30,000.00 target is not already covered by the €5,000.00 starting amount and its interest has to come from the monthly payments. The result is about €211.45 a month. The 3.5% rate is an example assumption, not a current market rate.

Assumptions

The interest rate stays constant for the whole term (your chosen scenario — real rates move).
The monthly contribution stays the same and is paid on time.
Interest is credited monthly at the nominal monthly rate and compounds from then on.
Tax, fees and inflation are not included.

Limitations of this calculator

A model calculation, not a forecast: the return you actually get depends on the real product.
One-off or changing contributions are not modelled — the plan assumes a constant monthly amount.
In 'duration' mode the year-by-year table is rounded up to whole months, so the target is slightly exceeded.
Tax on interest or investment income is not applied (version 1 calculates without tax).

Common misconceptions

Treating the rate as guaranteed: The rate is your assumption, not a current or guaranteed offer. Real rates vary and can change over the term.
Expecting a whole-month duration: In 'duration' mode the answer rarely lands on exact months; the table rounds up, so the target is reached a little early.
Reading the balance as spending power: The final balance is nominal, with no inflation, tax or fees taken off.
Assuming a goal is always reachable: Some combinations have no sensible answer — for example a target already met by the starting amount and interest alone.

Frequently asked questions

Which of the five figures can it work out?

The final balance, the monthly contribution, the duration, the starting amount or the interest rate needed. You choose the target figure at the top and enter the other four, so one tool answers 'what will I end up with?', 'how much must I save?' and 'how long will it take?'.

Why is the result slightly higher than an annual calculation?

Interest here is credited monthly. For the same nominal annual rate that ends a little higher than crediting once a year. Which applies depends on the account's terms.

What does 'start or end of the month' change?

A contribution at the start of the month earns that month's interest, so it ends slightly higher; at the end of the month, interest is credited first and the payment follows. The gap is small but grows with the term and the rate.

What does 'the goal is not reachable' mean?

Some combinations have no sensible answer — for instance when the target is already passed by the starting amount and interest alone, or when even a 100% rate falls short. The tool then points to the input you can change.

Are tax and inflation included?

No. This version calculates without tax, and the final balance is nominal, so it says nothing about future spending power. A separate inflation calculator covers purchasing power.

Sources and further reading

Official and independent sources on this topic. The links open each website in a new tab; no content is loaded from them into this page.

Savings Goal CalculatorU.S. Securities and Exchange Commission (Investor.gov)Official tool that works out the monthly amount needed to reach a savings goal from a starting sum, rate and timeframe.
Savings PlansMathematics LibreTexts (College Mathematics for Everyday Life)Reference for the savings-plan future-value formula and solving it for the required payment or the time to a goal.

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Last reviewed: 26/07/2026 · All calculations run in your browser – inputs are not stored. ·How we check our calculators