ISA Calculator & Optimizer
Compare Cash ISA vs Stocks & Shares ISA performance and find your optimal tax-free savings allocation for 2025/26.
Your Details
Total value of your existing ISA holdings
Maximum ~£1,667/month based on £20,000 annual ISA limit
Stocks & Shares allocation: 60%
Typical easy-access Cash ISA rates range from 3% to 5%
Long-term UK equities average ~7-8% per year
How long you plan to save in your ISA
Projected ISA Value
£93,047
After 10 years with a 40/60 Cash/Stocks split
Total Contributed
£60,000
Your deposits over the period
Total Growth
£28,047
Interest and investment returns
Tax Saved vs GIA
£302
Tax you would have paid outside an ISA
Projected Growth Over Time
Upcoming Change: Cash ISA Cap from 2027
The government has indicated that the Cash ISA annual subscription limit may be reduced from £20,000 to £4,000 from April 2027, with the remaining £16,000 only available for Stocks & Shares, Innovative Finance, or Lifetime ISAs. Consider this when planning your long-term ISA strategy.
This calculator is for informational purposes only and does not constitute financial advice. Tax calculations are based on current HMRC rates and may not reflect your exact circumstances. Always consult a qualified financial adviser.
Understanding ISAs: Cash ISA vs Stocks & Shares ISA
An Individual Savings Account (ISA) allows UK residents to save and invest up to £20,000 per tax year completely tax-free. There are no income tax, capital gains tax, or dividend tax charges on ISA returns, making them one of the most powerful tax-efficient savings vehicles available.
Cash ISA
A Cash ISA works like a savings account but with tax-free interest. Your capital is protected (up to FSCS limits), making it ideal for short-term savings or emergency funds. Current easy-access Cash ISA rates range from around 3% to 5% for the 2025/26 tax year.
Stocks & Shares ISA
A Stocks & Shares ISA lets you invest in funds, shares, bonds, and other assets with all gains and income completely tax-free. Historically, equities have returned around 7-8% per year on average, though past performance is not a guarantee of future returns. This ISA type is generally more suited to longer investment horizons of 5 years or more.
How to Split Your ISA Allowance
There is no single "right" split between Cash and Stocks & Shares ISAs. It depends on your risk tolerance, time horizon, and financial goals. A common approach is to keep 3-6 months of expenses in a Cash ISA as an emergency fund, then invest the rest in a Stocks & Shares ISA for long-term growth. Use the calculator above to model different scenarios and find the allocation that works best for you.
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Compare Cash ISA and Stocks & Shares ISA rates from UK providers. Tax-free saving made simple.
Compare ISA RatesCapital at risk. Tax treatment depends on individual circumstances and may change. This is not financial advice.