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: testing compounded growth on regular savings
Use these sample inputs as a quick scenario test, then change one variable at a time to compare outcomes.
| Input | Value |
|---|---|
| Opening balance | £10,000 |
| Monthly addition | £300 |
| Annual growth rate | 4.8% |
| Time horizon | 6 years |
The useful thing here is seeing how much extra the compounding adds by the later years. That often tells you whether to increase contributions or simply give the plan more time.
Method & assumptions
This calculator models savings growth using a future value formula that accounts for both an opening lump sum and regular monthly contributions, with interest compounded on the frequency you select. The calculation assumes the interest rate remains constant throughout the entire term, which is unlikely in practice — rates on savings accounts fluctuate with the central bank base rate and individual provider decisions. Results are shown in nominal terms and do not account for inflation, taxation, or FSCS protection limits (currently £85,000 per institution). The projections are illustrations only. savers are encouraged to review the AER on any account and to consider tax-efficient wrappers such as Cash ISAs or Lifetime ISAs for relevant goals.
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 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.
- UK ISA Guide 2026/27: Types, £20,000 Allowance, Transfers, LISAUK Individual Savings Account guide — Cash, Stocks & Shares, Lifetime and Innovative Finance ISAs, the £20,000 allowance, transfer rules and the 25% LISA bonus.