Investment Calculator
Projecting investment growth over years or decades means making an assumption about the return rate, and it is worth being upfront about what that assumption actually means — a single, constant annual rate applied smoothly every year, which is a useful modelling simplification but not how real investment returns actually arrive. This calculator projects your investment based on the rate, contributions and term you enter, while showing both the nominal projected value and a version adjusted for inflation, so the result reflects genuine purchasing power, not just a bigger number.
Investment Calculator
Project how your investments could grow over time — and see what your money could be worth in real terms.
Investments can go down as well as up. Past performance is not a guide to future results.
This Assumes a Steady Rate — Markets Don’t Work That Way
Real investment returns arrive as a genuinely bumpy sequence of good years and bad years, not a smooth, constant percentage applied every single year — a fund might rise 15% one year and fall 8% the next, averaging out to a similar long-term figure as a smooth 7% assumption, but the lived experience along the way is considerably more volatile than a calculator projection can show. This matters most for money you might need to withdraw during a downturn, since the order in which good and bad years happen, not just the average, can genuinely affect the final outcome for anyone drawing money out during the term rather than only investing throughout.
This is worth keeping in mind specifically so a smooth projection line is not mistaken for a promise — the destination shown here is a reasonable central estimate based on the assumption entered, not a guaranteed path, and the actual journey to any given end value will almost certainly look far less tidy along the way.
Why £100,000 in 20 Years Won’t Buy What £100,000 Buys Today
This calculator shows a real, inflation-adjusted value alongside the nominal projected figure, using a standard long-term inflation assumption, specifically because the nominal number on its own can be genuinely misleading over a long time horizon. A pound in twenty years buys meaningfully less than a pound today, even in a low-inflation environment, so a headline projected value that looks impressive in nominal terms can look considerably more modest once translated into today’s purchasing power — which is the number that actually matters for judging whether a long-term investment goal has genuinely been met.
This is particularly worth checking against a specific long-term goal, such as a retirement income target or a fixed future cost — comparing that goal against the real, inflation-adjusted figure rather than the larger nominal one gives a much more honest sense of whether a given contribution plan is actually on track.
Investments Aren’t Savings — And the Difference Matters
Unlike a savings account, where the rate is fixed and the capital is protected up to the FSCS limit, an investment can genuinely fall in value, sometimes considerably, and there is no guarantee the assumed growth rate reflects what actually happens. This is not a technicality — it is the fundamental trade-off behind why investments typically offer a higher long-term expected return than cash savings: that higher expected return compensates for genuinely taking on the risk of loss, not simply reflecting a better deal with no downside. Our Compound Interest Calculator models the equivalent growth for a fixed, guaranteed savings rate, which is worth comparing directly if you are weighing the two approaches against each other.
Nominal Versus Real, Side by Side
£10,000 invested with a further £200 a month, growing at 7% a year for 20 years, projects to a nominal total in the region of £144,500. Adjusted for 2.5% assumed annual inflation over the same period, the real, purchasing-power-equivalent value comes out closer to £87,700 — a meaningful gap purely from the effect of prices rising over two decades, not from anything going wrong with the investment itself. Both figures are correct; they simply answer different questions, and conflating the two is a common way long-term plans end up appearing more comfortable on paper than they will genuinely feel by the time the money is actually needed.
Where the Growth Actually Comes From
For a long-term investment, the growth is generally split between what you actually contribute and what compounding adds on top, and the balance between the two shifts considerably over time — in the early years, contributions dominate the growing total, while in later years, the compounding growth on an already large balance can start to outweigh new contributions considerably. This is part of why starting earlier tends to matter more than the exact monthly amount contributed, since time gives compounding more room to do the heavier lifting later in the term. Investing within a tax-free wrapper adds a further layer of benefit on top of the growth itself — our ISA Growth Calculator shows the equivalent projection sheltered from tax entirely.
Frequently Asked Questions
What return rate should I actually use?
There is no universally correct figure, but historic long-term UK stock market averages (before inflation) commonly sit in the region of 7-8% a year over multi-decade periods, though any single year, or even decade, can differ considerably from that long-run average.
Does this calculator account for investment fees?
No — it projects growth at the gross rate you enter. Platform fees, fund charges and any adviser fees would reduce the actual net return, so it is worth entering a rate that already reflects your expectation net of these costs, or treating the result as an upper estimate.
Is a lump sum or regular contributions better?
Investing a lump sum immediately generally has a higher expected long-term return than spreading it in gradually, purely because it has more time in the market, though regular contributions from ongoing income are simply the practical, available approach for most people building wealth over time rather than a strategic choice between two funded alternatives.
Should I reduce my assumed growth rate as I approach my target date?
Many investors do shift toward lower-risk, lower-expected-return assets as a goal approaches, precisely to reduce the risk of a poorly timed downturn shortly before the money is needed — this calculator uses a single constant rate throughout, so adjusting your assumption manually for a later, more conservative phase can give a more realistic late-term picture.
Can I lose money investing over the long term?
Yes — while diversified investments have historically tended to recover and grow over long periods, this is not guaranteed for any specific individual investment, timeframe or fund, and past performance is not a reliable predictor of future results.
Does diversification actually reduce risk?
Spreading investment across different assets, sectors and geographies generally reduces the impact of any single investment performing badly, though it does not eliminate market risk entirely — a genuinely widespread downturn can still affect a well-diversified portfolio, just typically less severely than a concentrated one.
Important Information
This calculator provides an estimate based on the assumptions you enter and does not constitute financial advice. Investments can fall as well as rise in value, and past performance is not a reliable indicator of future results. For advice specific to your circumstances, consult a qualified financial adviser. See our Disclaimer for further information.