Useful next calculations
Rates and sources
Compound growth assumes reinvested returns and no platform fees. Past performance is not a guide to future returns.
Source: FCA — Investment basics. Check the linked guidance and any live quote before acting.
When to use this calculator
- Before choosing between saving, investing or changing a contribution.
- When you want to compare cautious, base and optimistic return assumptions.
- When you need a projection before making a longer-term decision.
- When you want to see whether starting earlier or contributing more changes the outcome more.
Example: building a medium-term savings target
Use these sample inputs as a quick scenario test, then change one variable at a time to compare outcomes.
| Input | Value |
|---|---|
| Starting balance | £5,000 |
| Monthly contribution | £350 |
| Savings rate | 4.5% |
| Target period | 5 years |
The value of this example is seeing what comes from your own contributions versus the interest earned. That split is often what makes the next decision clearer.
Method & assumptions
This calculator projects savings growth using compound interest applied to an opening balance plus regular monthly or annual contributions. The rate you enter should be the AER (Annual Equivalent Rate) advertised by your savings account, as this standardises for compounding frequency. You can model fixed-rate bonds, easy-access accounts, or regular savers by adjusting the rate and contribution fields.
The calculator assumes the interest rate remains constant throughout the term, which may not reflect reality — particularly for easy-access accounts, where rates can change with little notice. It does not model tax on interest income beyond your ISA wrapper or personal savings allowance. For a conservative projection, consider entering a rate slightly below the current advertised rate to account for potential rate reductions. The tool does not include fees or account charges, which are uncommon for standard UK savings accounts but worth checking with your provider.
Common mistakes
- Assuming a constant return without checking a more conservative growth rate.
- Forgetting ongoing contributions, fees or tax wrappers where relevant.
- Focusing only on the final balance instead of the path required to reach it.
- Ignoring the drag of charges over a long period.
What to do next
- Test a cautious, expected and optimistic growth rate.
- Compare this result with related savings or retirement tools before committing more money.
- Consider charges and any tax wrapper that applies.
- If the projected balance falls short, increase the contribution until the result meets your goal.
Guides that use this calculator
- UK Mortgage Overpayments Guide: When to Clear Faster and When to Save CashHow mortgage overpayments work, when they save the most interest, when early repayment charges matter, and when your cash should stay liquid instead.
- UK Emergency Fund Guide: How Much to Save, Where to Keep It, and What Comes NextA practical emergency-fund guide covering target sizes, where to keep the money, how to build the buffer, and what to do once it is full.