UK savings calculator
How long to £100,000?
Set what you have, what you can add and what you expect to earn on it. The answer comes in two forms: the number the account will show, and what that money will be worth by the time you get there.
Why there are two answers
£100,000 in twenty years is not £100,000. At 3% inflation it buys what about £55,000 buys today. The cash figure is what your account will show; the inflation-adjusted one is closer to what you can spend. We show both, and we put today’s money first in the results.
The annual growth rate is converted to a proper monthly equivalent instead of being divided by twelve. Dividing by twelve turns a 12% assumption into 12.68% by the end of the first year, and that error compounds every year after. Many calculators do it that way; we do not.
Questions
Two answers, and which one to believe
Why are there two answers, and which one is real?
Because £100,000 in fifteen years buys less than £100,000 today. The first answer is when the balance on screen hits the target. The second is when that balance has kept pace with inflation and matches the target in today's money.
We treat the second as the useful one, and many calculators publish only the first. At £200 a month the gap is about twenty-one years. The cash figure arrives in 22 years 10 months; the inflation-adjusted one in 43 years 8 months. Showing only the cash date is the flattering version, so we show both.
What growth rate should I assume?
Nobody knows, and a site that picks one number with certainty is guessing. The calculator defaults to 5 per cent a year as a middle assumption, not as a forecast.
Moving the slider is often more instructive than the headline date. The timeline shifts far more when you change what you pay in than when you nudge the return assumption. Two percentage points on growth might move the answer by a couple of years; doubling the contribution can cut it in half.
One technical detail matters over long horizons. We convert the annual rate to its true monthly equivalent instead of dividing by twelve. Dividing by twelve and compounding monthly turns a 5 per cent headline into slightly more than 5 per cent, which adds up over decades.
Where does the money sit while it grows?
For a pot this size, an ISA often absorbs the contributions. £20,000 can go into ISAs in the 2026 to 2027 tax year, which is more than £1,600 a month, above any preset on this page. Growth and withdrawals inside an ISA are untaxed.
If you are saving for a first home, a Lifetime ISA comes with a government bonus: £4,000 a year, with a 25% bonus up to £1,000. It counts towards the £20,000 ISA limit. On £200 a month the bonus can outweigh small differences in investment return. It also has strings attached: pay in before 50, open before 40. withdrawing for anything other than a first home or age 60 carries a charge.
Which wrapper fits a household depends on income, timing and what else you hold. This page does not collect that detail.
Does the calculator account for tax, fees or pay rises?
No, and we say that up front. It models one pot, one monthly contribution and one growth rate. Platform fees, fund charges, tax outside a wrapper and rising pay over time are all left out.
Fees and tax on unwrapped investments push the date later; increasing contributions pull it earlier. A simpler model with clear gaps beats a busy one that hides its assumptions.
The Swealth letter
One letter a week, on Thursday
Plain writing about British money, and the UK Wealth Blueprint to start with.