ISA calculators
Run the numbers.
Six calculators for the questions ISA investors actually ask: what your ISA could grow to, what fees really cost, how much allowance you have left, the tax an ISA saves you, what a Lifetime ISA adds, and how far a fall has to recover. Every result is an illustration, not a forecast.
What could your ISA be worth?
Put in what you have now, what you can add each month and how long you'll leave it. See how much of the final figure is your own money and how much is growth.
Your numbers
Illustrative value after 25 years
£0
How to read this
Your monthly amount is added at the end of each month, any extra yearly top-up at the end of each year, and the whole pot grows at the same steady rate every year. Real markets never behave that neatly, but the shape is honest: early on most of the pot is your own money, and the longer you leave it, the more of it is growth on growth. I explain why in the maths that changes everything, and why what you put in matters so much in why savings rate matters more than returns. Figures are before inflation.
What do fees really cost?
Compare a platform that charges a percentage of your pot with one that charges a flat monthly fee, both holding the same fund. Small numbers, compounded for decades, become big ones.
Your numbers
Option A: percentage platform
Option B: flat-fee platform
Illustrative value after 25 years
A · Percentage fee
£0
B · Flat fee
£0
How to read this
Charges are taken monthly from the pot, so every pound paid in fees also stops earning growth for the rest of the period. That is why the true cost is far bigger than the fees you can see on a statement. Percentage fees tend to suit smaller pots and flat fees larger ones; where the line falls depends on your numbers. More on this in why fees decide your returns.
How much allowance do you have left?
Add up what you've paid into each type of ISA this tax year. The allowance resets on 6 April, and anything unused is gone.
This tax year
Allowance left this tax year
£0
How to read this
The £20,000 is one allowance shared across all your ISAs, not £20,000 for each. Transferring an existing ISA from one provider to another does not use any allowance, as long as it's done as a proper transfer. A Junior ISA has its own separate allowance (£9,000 at the time of writing) and doesn't count towards yours. More in how the ISA allowance works and the ISA family explained.
How much tax does an ISA save?
The same investments held outside an ISA can be taxed on their dividends and on the gains when you sell. Inside an ISA, neither applies. Here's the difference for one year.
Your numbers
Tax an ISA would save this year
£0
How to read this
Rates and allowances used, for 2026/27 at the time of writing: a £500 dividend allowance, then dividend tax of 10.75% (basic), 35.75% (higher) or 39.35% (additional); a £3,000 Capital Gains Tax allowance, then 18% for basic-rate taxpayers and 24% for higher and additional. It assumes you haven't used those allowances elsewhere, and treats a basic-rate taxpayer's whole gain at 18%, although a large gain can push part of it to 24%. Check gov.uk for the current figures. And the saving repeats every year the money stays wrapped, which is the real point. More in what a Stocks and Shares ISA is.
What does a Lifetime ISA add?
The government adds 25% to what you pay in, up to £1,000 a year, from your first payment until you turn 50. See what that could add up to, and what it costs to withdraw for anything other than a first home or reaching 60.
Your numbers
Withdrawing for another reason
Illustrative value at 50
£0
Penalty-free withdrawals: towards your first home (costing £450,000 or less, with your first payment made at least 12 months before), from age 60, or if you're terminally ill.
How to read this
Rules at the time of writing: you must be 18 to 39 to open one and make your first payment before 40; you can pay in until 50; the bonus is 25% up to £1,000 a year; withdrawing for any other reason costs 25% of the amount taken, which takes back the bonus and about 6.25% of your own money on top. The Lifetime ISA is proposed to be replaced by a new First-Time Buyer ISA, so check gov.uk for the current rules. More in the Lifetime ISA explained.
How far does a fall have to recover?
A fall and the rise needed to undo it are not the same size. Lose 20% and you need a 25% rise just to get back to where you started. This is the percentage maths behind “don’t sell in a panic”.
Your numbers
Rise needed to get back to even
0%
| Fall | Rise needed |
|---|
How to read this
Selling after a fall turns a loss on paper into a real one and takes you out of the recovery, and missing the recovery is what does the lasting damage. That's the mechanism behind the behaviour gap, and why the answer to should you cash in your ISA is rarely “when markets fall”. Past recoveries are no guarantee of future ones.
New to ISAs?
Read the fifteen articles in order.
Getting Started takes you from the basics to opening your ISA, then the principles that keep you invested and how wealth builds over time.
Go to Getting StartedAll results are illustrations, not forecasts, and not financial advice. They assume steady rates that real markets never deliver. The value of investments can go down as well as up, and you can get back less than you put in. Allowances, tax rates and ISA rules can change, so always check gov.uk for the current figures.
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