Project how your savings grow with compound interest and regular monthly deposits.
| Initial deposit | — |
| Monthly deposits | — |
| Total deposited | — |
| Compound frequency | — |
| Annual interest rate (AER) | — |
| Savings period | — |
| Total interest earned | — |
| Year | Deposited | Interest | Cumulative Interest | End Balance |
|---|
This calculator uses the standard compound interest formula to project how a savings account grows over time. Both your initial deposit and regular monthly contributions are factored in, along with the compound frequency of your account.
The final balance is calculated as:
Balance = P × (1 + r/n)nt + PMT × [(1 + r/n)nt − 1] ÷ (r/n)
Where P is the initial deposit, r is the annual interest rate, n is the compounding frequency per year, t is the number of years, and PMT is the regular deposit per period. Monthly deposits are treated as end-of-period payments.
Interest that compounds monthly grows slightly faster than interest that compounds annually at the same headline rate. This is because monthly compounding applies interest to interest more frequently. Banks in the UK typically express rates as AER (Annual Equivalent Rate), which accounts for compounding — so two accounts with the same AER will grow at the same rate regardless of how often they technically compound. When using this calculator, enter the AER shown on your account.
| Account type | Access | Typical rate (2026) | Best for |
|---|---|---|---|
| Easy access | Instant | 4.0–5.0% AER | Emergency fund |
| Notice account | 30–120 days | 4.5–5.2% AER | Medium-term savings |
| Fixed-rate bond | At term end | 4.5–5.5% AER | Lump sum you won't need |
| Cash ISA | Varies | 4.0–5.0% AER | Tax-free savings |
| Regular saver | At term end | 5.0–8.0% AER | Monthly saving habit |
Interest earned outside an ISA is subject to income tax above your Personal Savings Allowance:
With savings rates at 4–5%, a basic rate taxpayer earning more than £1,000 in interest would need a pot of around £20,000–£25,000 before tax becomes a concern. At that point, moving savings into a Cash ISA makes clear sense.
Each adult can save up to £20,000 into ISAs per tax year (6 April to 5 April). Interest inside a Cash ISA is completely tax-free and does not affect your PSA. You can hold a Cash ISA alongside other ISA types, as long as total contributions stay within £20,000. Unused allowance cannot be carried forward to the next tax year.
Time is the most important variable in any savings projection. £200/month saved for 30 years at 4.5% produces nearly three times more interest than £200/month saved for 15 years — not twice as much, because compound interest accelerates over time. Even small regular deposits started early consistently outperform larger deposits started later.
Three realistic UK savings scenarios — all projected with monthly compounding and end-of-period deposits.
All projections assume the stated interest rate is maintained for the full period and contributions are made every month. Actual rates on variable accounts will fluctuate. Not financial advice.