CalculatorsSwitch calculator
How this works
The calculator starts with what you have now and steps forward one month at a time. Each month your pot grows by the yearly return, turned into a monthly rate, and then your monthly amount goes in. It stops when the balance reaches your target and tells you how long that took.
You can raise your monthly amount once a year, for example in line with pay rises, and you can switch to today’s money. That uses the return after inflation, so the target keeps today’s buying power.
What it assumes
- Returns are smooth and steady. Real markets rise and fall, sometimes sharply.
- Fees and tax aren’t included. Investing through an ISA or pension keeps growth tax-free.
- It stops looking after 100 years.
Worked example
£5,000 now plus £500 a month at 7%
- Reaching £1,000,000 takes 36 years 4 months. You pay in £223,000 and growth adds £780,261.
- In today’s money, with inflation at 3.1%, the return drops to about 3.78% a year and it takes 52 years 5 months.
- Raise your £500 by 3% each year and you get there in 32 years 1 month instead, more than four years sooner.
Worked out with the same maths as the calculator above.
What to do next
Common questions
What return should I use?
There’s no right answer, because nobody knows future returns. Many people try 5% to 7% a year before inflation for a mix of global shares, then try lower figures to see how sensitive the result is.
Should I look at today’s money?
Yes, at least once. A million pounds in 40 years will buy much less than it does now. Switching to today’s money shows how long it takes to reach the same buying power.
What makes the biggest difference?
Time and how much you pay in. Starting earlier gives growth longer to work, and raising your monthly amount each year cuts years off, as the example shows.
How much can I put into an ISA each year?
The ISA allowance is £20,000 for 2026/27, split however you like across ISA types. Pensions have their own, separate allowance.