Cash ISA Savings Calculator
Estimate how your tax-free ISA savings could grow over time with compound interest and regular monthly contributions.
Year-by-year projection
| Year | Total Paid In | Interest Earned | Projected Balance |
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Why use a cash ISA savings calculator?
A cash ISA lets UK savers earn interest tax-free. That sounds simple, but the real power comes from compounding over years. This calculator helps you model that growth with your own assumptions: monthly savings, interest rate, timeframe, and even contribution increases over time.
If you're trying to compare a cash ISA with a standard savings account, a calculator is useful because small differences in tax and interest can compound into meaningful gaps later.
What this calculator shows
1) Projected final balance
This is your estimated ISA value at the end of your chosen term, combining your deposits and compound interest.
2) Total paid in vs interest earned
You can separate your own contributions from growth. This helps you understand how much of your future balance comes from disciplined saving versus returns.
3) Inflation-adjusted value
Money in the future may buy less than it does today. The calculator estimates your final balance in today's purchasing power using your inflation assumption.
4) Taxable account comparison
The tool also estimates what might happen if you saved at the same headline rate in a taxable account. This gives a rough view of the potential value of tax-free ISA sheltering.
How the cash ISA projection works
The model converts your annual rate and compounding frequency into an effective monthly rate, then simulates each month of saving. It applies interest, adds your monthly contribution, and repeats until the end of your selected term.
- Initial deposit starts compounding immediately.
- Monthly contributions are added at month end.
- If you set annual contribution growth, monthly saving rises once per year.
- A year-by-year table shows your running progress.
Cash ISA rules (quick UK refresher)
- Interest in a cash ISA is tax-free.
- The annual ISA allowance is currently £20,000 (can change in future tax years).
- You can split allowance across ISA types, subject to current HMRC rules.
- Some ISAs are flexible; others are not. Check provider terms before withdrawing and re-depositing.
This calculator includes an allowance warning if your modelled annual contributions exceed £20,000.
Ways to improve your ISA results
Automate deposits
Standing orders reduce decision fatigue and improve consistency. Consistency matters more than trying to perfectly time rates.
Increase contributions with income
Even a small annual increase in monthly saving can substantially lift long-term outcomes.
Compare providers regularly
Cash ISA rates change. A transfer to a stronger rate (without breaking ISA rules) can improve returns.
Keep emergency cash accessible
Choose an easy-access ISA if you may need funds. If your timeline is longer and you can lock money away, fixed-rate options may pay more.
Common limitations of any savings calculator
- Rates are not guaranteed unless fixed by product terms.
- Inflation is uncertain and can vary year to year.
- Tax treatment and ISA rules can change.
- Real account conditions (bonuses, transfer windows, restrictions) may differ.
FAQ
Is a cash ISA always better than a normal savings account?
Not always. If you pay little or no tax on savings interest, a top non-ISA account can sometimes beat a cash ISA rate. Compare after-tax outcomes.
Can I use this as an ISA interest calculator for monthly savings?
Yes. Enter your monthly amount, expected rate, and term. The tool calculates a monthly compounding projection and provides a full breakdown.
Does this calculator give financial advice?
No. It's an educational planning tool. For personal recommendations, speak with a regulated financial adviser.