Put in a starting balance, what you add each month, the rate and how long, and see the interest and final pot, with the tax rules that apply.
Final balance = your starting money and monthly deposits, grown by compound interest. The interest earned is the balance minus everything you paid in.
Interest is compounded monthly from the AER you enter (the rate that already includes a year's compounding). Every month you earn interest on your balance and on the interest already added, which is why the pot grows faster the longer you leave it.
Tax: inside a Cash ISA the interest is entirely tax-free. Outside one, the Personal Savings Allowance lets basic-rate taxpayers earn £1,000 of interest a year tax-free, and higher-rate taxpayers £500 (additional-rate taxpayers get nothing). Interest above your allowance is taxed at your income tax rate.
Illustrative only. Assumes a constant rate and monthly compounding; the figure shown is gross interest before any tax.
From 6 April 2027 a flat 22% charge applies to interest paid on cash held inside a non-Cash ISA, which in practice means the cash sitting in a Stocks and Shares ISA. It also covers equivalent alternative finance returns.
Three things make it unusual, and worth knowing before it starts:
Source: HMRC, ISA reform 2027 anti-circumvention rules factsheet. Announced policy, in force from 6 April 2027; we re-check this page if the detail changes.
Illustrative only, not financial advice. Assumes a constant interest rate and monthly compounding; the interest shown is gross, before any tax. Real savings rates change over time. Your capital in cash is not at market risk, but inflation can erode its buying power. Always do your own research.
For investment growth instead, see Compound Growth; to set a target, the Emergency Fund calculator.