Goal-seek
Investment goal calculator: how much to invest
Tell us your target, expected return and timeframe, and we solve for the monthly contribution you need — then show the full year-by-year projection that gets you there.
Solve for your monthly contribution
We use the closed-form annuity formula and verify it with a forward projection.
To reach £250,000 in 20 years at 7% you need to invest
£441.15 / month
Projected ending balance with that contribution: £250,000
Future value
£250,000
Total contributions
£110,876
Investment growth
£139,124
Balance over time
Stacked: your contributions vs. compounded growth.
Year-by-year breakdown
| Year | Balance | Contributions | Growth |
|---|---|---|---|
| 1 | £10,828 | £10,294 | £534.64 |
| 2 | £17,078 | £15,588 | £1,491 |
| 3 | £23,780 | £20,881 | £2,898 |
| 4 | £30,966 | £26,175 | £4,791 |
| 5 | £38,671 | £31,469 | £7,202 |
| 6 | £46,934 | £36,763 | £10,171 |
| 7 | £55,794 | £42,057 | £13,737 |
| 8 | £65,294 | £47,350 | £17,944 |
| 9 | £75,481 | £52,644 | £22,837 |
| 10 | £86,405 | £57,938 | £28,467 |
| 11 | £98,118 | £63,232 | £34,886 |
| 12 | £110,678 | £68,525 | £42,152 |
| 13 | £124,145 | £73,819 | £50,326 |
| 14 | £138,587 | £79,113 | £59,474 |
| 15 | £154,072 | £84,407 | £69,666 |
| 16 | £170,677 | £89,701 | £80,977 |
| 17 | £188,482 | £94,994 | £93,488 |
| 18 | £207,575 | £100,288 | £107,287 |
| 19 | £228,047 | £105,582 | £122,465 |
| 20 | £250,000 | £110,876 | £139,124 |
Plan backwards from your goal
Most calculators ask what you will end up with. Goal-seek flips the question: decide the number you want — a house deposit, a retirement pot, a passive-income target — and find out what it takes to get there. Knowing the monthly figure turns a vague ambition into a concrete plan.
Already saving something? Raise your starting amount and watch the required monthly contribution fall, thanks to the head start compounding on day one.
How compounding works
Compounding is growth on growth. Each period, your returns are added to your balance — and the next period earns returns on that larger balance too. Over long horizons this snowball effect dwarfs your original contributions.
A lump sum grows by FV = PV × (1 + r)ⁿ, where r is the periodic rate and n the number of periods. Monthly compounding splits the annual rate into twelve.
Regular deposits form an annuity:FV = PMT × [(1 + r)ⁿ − 1] / r. We add contributions at the end of each period (ordinary annuity).
With DRIP, dividends buy more shares, which pay more dividends. Add dividend growth and your yield on cost rises year after year — the engine behind real passive income.
Why time matters more than rate
Invest £10,000 at 7% with no further deposits and you have roughly £19,672 after 10 years, but about £76,123 after 30 years. The extra two decades did far more than the first one — because each year compounds on an ever-larger base. Starting earlier usually beats trying to earn a higher return.
Pick the right calculator
One engine, four lenses. Each mode tailors the inputs and outputs for a specific question — all using the same correct compounding math.
Ready to put compounding to work?
A projection only matters once you start investing. These are starting points to research a broker or ETF platform that suits you. We are not recommending a specific product — compare fees, eligibility and protections before you commit.
Affiliate disclosure: some links may be sponsored and we may earn a commission at no cost to you. This is not financial advice.
Frequently asked questions
How does the investment goal calculator work?
You enter a target future value, an expected annual return, your starting amount and a timeframe. Using the closed-form annuity formula PMT = [FV − PV(1 + r)ⁿ] × r / [(1 + r)ⁿ − 1], it solves for the monthly contribution required, then runs the forward projection to confirm the answer reaches your target.
How much do I need to invest to make £1,000 a month in passive income?
As a rough guide, dividing your desired annual income by a sustainable yield gives the portfolio size. For £1,000 a month (£12,000 a year) at a 4% yield you would need around £300,000. Set that as your target here to see the monthly contribution required to build it.
Is the required contribution guaranteed to hit the target?
Only if your actual return matches the rate you entered, which is never guaranteed. Markets fluctuate. Treat the figure as a planning baseline and revisit it as your returns and circumstances change.
What if I can already invest more than the required amount?
Great — you will reach the goal sooner or exceed it. Reduce the number of years or raise the target to explore how a higher contribution changes the timeline.