Calculators
Investment Growth Calculator
Model the long-term growth of an investment with a starting amount, monthly contributions and an assumed annual return.
Projected value
£130,313
You contributed
£70,000
Compound growth
£60,313
Past performance is not a reliable indicator of future returns.
Build a portfolio around this goal.
How this calculator works
Compound growth is the engine of long-term investing: the returns you earn this year generate their own returns next year, and so on. Over 20–30 years, the difference between a portfolio that compounds and one that sits in cash is enormous.
This calculator takes a starting amount, an optional monthly contribution, an annual growth rate (net of charges), and a time horizon. It compounds monthly and shows you the final value, the total you contributed, and the share that came from growth.
What it doesn't model is sequence risk, tax wrappers (ISA vs general account vs pension), withdrawals, or the impact of fees that compound the same way returns do. A 1% extra annual charge can cost a third of your pot over 30 years — choosing the right portfolio matters.
Assumptions & limitations
- Growth is annual, net of charges, compounded monthly
- Monthly contributions are paid at the start of each month
- No tax is deducted (results approximate an ISA or pension)
- No withdrawals during the term
The value of pensions & investments and any income from them can fall as well as rise and you may not get back the original amount invested.
Worked examples
Indicative figures based on the rates above. Your situation may differ — speak to an adviser before relying on these numbers.
£10,000 lump sum, 20 years at 5% net
Set and forget — no monthly contributions, mid-range growth assumption.
Projected value: £27,126.40. Contributions £10,000, growth £17,126.40.
£200 per month for 15 years at 6% net
Steady monthly investing, typical balanced portfolio assumption.
Projected value: £58,454.37. Contributions £36,000, growth £22,454.37.
£25,000 starting pot plus £300/month for 25 years at 5%
Lump sum combined with regular contributions inside a long-term plan.
Projected value: £266,375.40. Contributions £115,000, growth £151,375.40.
£50,000 ISA for 10 years at 4% net
Cautious portfolio over a shorter horizon — closer to a planning floor.
Projected value: £74,541.65. Contributions £50,000, growth £24,541.65.
Common questions
Is compound interest really that powerful?+
Yes — £200 a month compounded at 5% net over 30 years becomes around £166,000, of which only £72,000 is contributions. The rest is compound growth.
What rate of return should I assume?+
For a diversified portfolio over a long horizon, 4–6% real (after inflation) has historically been a sensible planning assumption — but actual returns vary, and past performance is not a reliable indicator of future returns.
Should I invest in an ISA or pension?+
Often both. ISAs give tax-free growth and flexible access; pensions give tax relief on contributions but lock the money up until age 55 (rising to 57). The right balance depends on your goal and tax position.
How much do fund charges actually matter?+
A lot. A 1.5% total charge vs 0.5% compounds against you exactly the same way returns compound for you — and over 30 years can cost a third of your final pot.
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Want this applied to your situation?
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The value of pensions & investments and any income from them can fall as well as rise and you may not get back the original amount invested.