Compound interest calculator

It depends entirely on where the money's held. UK easy-access savings rates and cash ISAs have typically ranged from under 1% to around 5% depending on the wider interest rate environment; stocks & shares investments have historically returned more over the long run (often cited around 5-7% after inflation) but with real risk of loss, especially over shorter periods. Use a rate that matches the actual account or investment you're modelling, not a generic assumption.

No — these are gross growth figures before any tax. Interest earned outside a tax-free wrapper like an ISA may be taxable depending on your Personal Savings Allowance; see the Savings Tax calculator to check. Growth inside a Cash ISA, Stocks & Shares ISA, or pension is tax-free (or tax-deferred), which is exactly why they're worth using where you can.

Interest is only earned on the balance you've built up so far, which starts small — most of an early year's growth is simply your own contributions landing in the account. As the balance grows, the interest portion grows with it, which is the compounding effect actually taking hold; give it time.

This calculator answers "where do these contributions get me" — for the reverse question, "how much do I need to save each month to reach a target", use the Savings Goal calculator instead.