How to Calculate ISA
What is ISA?
An ISA (Individual Savings Account) is a tax-free wrapper for savings and investments. Any growth, interest, or dividends earned within an ISA are completely free from Income Tax and Capital Gains Tax — forever. The annual allowance is £20,000 per person (2024/25). Unused allowance cannot be carried forward.
Formula
- FV
- PV × (1+r)^n + PMT × ((1+r)^n − 1)/r — PV × (1+r)^n + PMT × ((1+r)^n − 1)/r
- PV
- PV value — Variable used in the calculation
- PMT
- PMT value — Variable used in the calculation
Step-by-Step Guide
- 1Contribute up to £20,000 per tax year (April 6 – April 5)
- 2Stocks and Shares ISA: invest in funds, shares, ETFs — suitable for 5+ year horizons
- 3Cash ISA: earn interest tax-free — better than regular savings account for higher-rate taxpayers
- 4Lifetime ISA (LISA): 25% government bonus on up to £4,000/year — for first home or retirement
- 5Compound growth formula: FV = PV × (1+r)^n + PMT × ((1+r)^n − 1)/r
Worked Examples
Frequently Asked Questions
What is Isa?
An ISA (Individual Savings Account) is a tax-free wrapper for savings and investments. Any growth, interest, or dividends earned within an ISA are completely free from Income Tax and Capital Gains Tax — forever
How accurate is the Isa calculator?
The calculator uses the standard published formula for isa. Results are accurate to the precision of the inputs you provide. For financial, medical, or legal decisions, always verify with a qualified professional.
What units does the Isa calculator use?
This calculator works with inches, British pounds, percentages. You can enter values in the units shown — the calculator handles all conversions internally.
What formula does the Isa calculator use?
The calculator applies the standard formula for this type of calculation. See the 'How It Works' steps above for the detailed formula breakdown.
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