ISA Calculator

Calculate how much your ISA could be worth over time and see the tax savings compared to a standard savings account.

ISA Details
£
£
Max £1,666.67/month to stay within allowance
years
Expected Returns
% AER
Current best rates: 4-5% AER
% pa
Historical average: 7-10% pa
% pa
Typical range: 0.15-0.45%
Your Tax Status (for comparison)
Affects savings interest tax outside ISA
Understanding ISAs
What is an ISA?

An Individual Savings Account (ISA) is a tax-efficient savings wrapper. Any interest, dividends, or capital gains earned within an ISA are completely tax-free - you never have to declare them on your tax return.

Types of ISAs
  • Cash ISA: Like a savings account but tax-free. Low risk, guaranteed returns.
  • Stocks & Shares ISA: Invest in funds, shares, and bonds tax-free. Higher potential returns but capital at risk.
  • Lifetime ISA: For first home or retirement. 25% government bonus on up to £4,000/year.
  • Innovative Finance ISA: Peer-to-peer lending within an ISA wrapper.
ISA Rules
  • Must be 18+ for Stocks & Shares ISA (16+ for Cash ISA)
  • Must be UK resident
  • Can contribute to one of each type per tax year
  • Unused allowance doesn't roll over
  • Can transfer between providers without affecting allowance
Cash ISA vs Stocks & Shares ISA
Cash ISA Stocks & Shares ISA
Risk Level Very Low Medium to High
Typical Returns 3-5% AER 5-10% pa (variable)
Best For Short-term (1-3 years) Long-term (5+ years)
Access Usually instant Few days to sell
ISA Allowances 2026/27
Total ISA Allowance £20,000
Lifetime ISA Limit £4,000
Junior ISA Limit £9,000

Allowances apply per tax year (6 April to 5 April)

Personal Savings Allowance

Outside an ISA, you can earn some interest tax-free:

Basic rate taxpayer £1,000
Higher rate taxpayer £500
Additional rate taxpayer £0

ISA interest doesn't count towards this allowance

ISA Tips
  • Use your full £20k allowance each year if possible
  • Consider Stocks & Shares ISA for 5+ year goals
  • Cash ISA for short-term savings or emergency fund
  • Compare platform fees - they eat into returns
  • Low-cost index funds often beat active funds
  • Transfer old ISAs to get better rates/funds
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