Calculator
Compound Interest Calculator
Visualize how regular savings grow over time with compound interest.
Try it nowCalculate the long-term compounding cost of the new £12,000 Cash ISA cap for under-65s introduced in the UK Autumn Budget 2025. Model the difference of redirecting excess contributions above £12,000/year to taxable accounts.
How to Use This Tool:
- Enter your current Cash ISA balance and expected interest rate.
- Input your planned monthly contribution and your age.
- Select your marginal savings interest tax rate (20%, 40%, or 45%) to see the projected wealth loss.
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Important Financial Calculation Disclaimer & Sources
Scope & Estimative Nature:
- Assumes a constant interest rate and constant tax rates throughout the projection period.
- Does not model the Personal Savings Allowance (PSA) deductions, which vary by income level.
Official Data Sources:
- HM Revenue & Customs (HMRC) ISA subscription limits guidance
- UK Autumn Budget 2025 policy documents
Methodology:
- Inputs are normalized into numeric values in the browser.
- The matching FinanceUp calculation engine runs standard formulas for the selected tool.
- Results are formatted using United Kingdom currency, locale, and available country rules.
- Charts, tables, and result cards are derived from the same calculation output to keep the page internally consistent.
All calculations are estimates. Tax rates, retirement regulations, and investment fees change over time. Please verify critical values with an official professional advisor or reference the official publications cited above before taking action.
Guide & How-To
AI Overview
To calculate cash isa 2027 cap impact calculator in United Kingdom (2026): Calculate the long-term compounding cost of the new £12,000 Cash ISA cap for under-65s introduced in the UK Autumn Budget 2025. Model the difference of redirecting excess contributions above £12,000/year to taxable accounts. The calculation is performed by applying the latest local rules, standard deductions, brackets, or compounding terms to your inputs to provide an instant, accurate estimate.
The 2027 Cash ISA Cap Reform Explained?
Announced in the UK Autumn Budget 2025 and starting April 6, 2027, savers aged 65 and under will see their annual Cash ISA subscription limit cut from £20,000 to £12,000. While the total ISA allowance remains at £20,000, the remaining £8,000 must be directed to non-cash accounts (like Stocks & Shares ISAs) to remain tax-free. Contributions beyond the £12,000 cash cap that are held in cash will be subject to taxation.
The Cost of Taxable Interest Compounding?
Under the new rules, any cash savings contributions exceeding £12,000 per year (or £1,000 per month) that cannot be directed to stocks must be placed in a standard taxable savings account. The interest earned on these funds is subject to income tax based on your tax band, which severely dampens the compounding growth compared to a tax-free Cash ISA over 10, 20, or 30 years.