Set a starting pot, a monthly amount and a return. Watch compounding do the heavy lifting — the number updates live.
Each month your pot earns a slice of the annual return, then the new total earns a return next month — that's compounding. Future value ≈ starting pot grown for the period + every monthly payment grown from the date you made it. The longer the time, the more of the final pot is growth rather than the cash you put in.
Example: £200/month for 30 years at 5% after inflation grows to about £166,000 — yet you only paid in £72,000. The other ~£94,000 is compound growth. Start ten years earlier and the same £200 lands far higher: time beats amount.
A 5% real return is a common long-run assumption for a global equity fund (~7% before inflation). Returns are not guaranteed; markets fall as well as rise. Inside an ISA this growth is tax-free (£20,000/yr allowance in 2026/27).
Illustrative only — not financial advice. This models steady monthly contributions compounding at a constant annual return; real returns vary year to year, and fees, tax and inflation all affect the outcome. Your capital is at risk — investments can fall as well as rise. Figures use the 2026/27 tax year. Always do your own research or speak to a qualified adviser.
See also the 2026/27 tax rates. © The Base Rate · Calculators · About · Contact · @the_baserate