UK Investment calculator
Project how an investment grows with monthly contributions and market returns — choose an index preset or your own rate, in nominal or inflation-adjusted terms.
Investment plan
Presets reflect long-run historical averages before fees and tax. Markets are volatile — real returns vary widely year to year.
| Year | Contributed | Balance |
|---|---|---|
| 1 | £16,000.00 | £17,329.91 |
| 2 | £22,000.00 | £25,427.37 |
| 3 | £28,000.00 | £34,372.73 |
| 4 | £34,000.00 | £44,254.79 |
| 5 | £40,000.00 | £55,171.63 |
| 6 | £46,000.00 | £67,231.60 |
| 7 | £52,000.00 | £80,554.41 |
| 8 | £58,000.00 | £95,272.29 |
| 9 | £64,000.00 | £111,531.33 |
| 10 | £70,000.00 | £129,492.90 |
| 11 | £76,000.00 | £149,335.29 |
| 12 | £82,000.00 | £171,255.43 |
| 13 | £88,000.00 | £195,470.89 |
| 14 | £94,000.00 | £222,222.03 |
| 15 | £100,000.00 | £251,774.37 |
| 16 | £106,000.00 | £284,421.22 |
| 17 | £112,000.00 | £320,486.62 |
| 18 | £118,000.00 | £360,328.54 |
| 19 | £124,000.00 | £404,342.43 |
| 20 | £130,000.00 | £452,965.15 |
Past performance doesn't guarantee future returns. Fees, taxes, and timing all reduce real-world results. Estimates only — not financial advice.
Understanding your inputs
- Starting amount
- Your initial lump sum before any monthly investing.
- Monthly contribution
- What you invest each month on top of the starting amount.
- Time horizon (years)
- How long the money stays invested and compounding.
- Expected return
- A historical preset (stock index, balanced, conservative) or your own custom rate.
- Custom annual return
- Your own assumed yearly return when not using a preset.
Understanding your results
- Final value
- Projected portfolio value at the end — shown in today's money if inflation adjustment is on.
- You contribute
- The total you personally pay in across the whole period.
- Investment growth
- The portion of the final value created by returns rather than contributions.
How investment growth is projected
The projection compounds your starting amount and monthly contributions at the chosen annual return, month by month. The presets anchor to long-run history: broad US stock indexes have averaged roughly 10% per year nominal (about 7% real) over many decades, classic 60/40 portfolios nearer 8%, and conservative allocations around 5%. These are averages across long horizons — not promises, and not predictions for any particular decade.
Worked example
$10,000 starting plus $500/month for 20 years:
- At 10% nominal: roughly $450,000 — about $130,000 contributed, the rest growth
- At 8%: roughly $343,000
- At 5%: roughly $233,000
The spread between assumptions is the single biggest uncertainty in any long-term plan — always test your plan at a rate below the historical average.
Nominal vs real returns
A nominal projection counts currency units; a real (inflation-adjusted) projection counts purchasing power. At 2.5% inflation, $1,000,000 in 30 years buys what about $480,000 buys today. For retirement and other distant goals, the "today's money" toggle gives the more honest picture — and pairs the expected return down by the same inflation assumption.
What this model ignores
- Volatility and sequence risk — real portfolios don't grow in a straight line, and the order of good and bad years matters when you're withdrawing.
- Fees — a 1% annual fee consumes roughly a quarter of a portfolio's final value over 30 years versus a 0.1% index fund.
- Tax — use tax-sheltered accounts (401(k)/IRA, ISA, RRSP/TFSA, super) before taxable ones.
For regular-deposit savings at a bank rate, the savings calculator is the better tool; for one-off return on a single investment, see the ROI calculator.
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Frequently asked questions
What return should I assume for investments?
How much will $500 a month grow in 20 years?
Should I look at nominal or inflation-adjusted returns?
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