Continue your plan
Useful next calculations
Rates & 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: seeing compounding do the heavy lifting
Use these sample inputs as a quick scenario test, then change one variable at a time to compare outcomes.
| Input | Value |
|---|---|
| Starting amount | £15,000 |
| Monthly contribution | £250 |
| Annual return assumption | 6.5% |
| Investment period | 10 years |
This example works because it shows how a steady contribution plan compounds more meaningfully in the later years. That makes the trade-off between time and return easier to judge.
How to read your results
Total
The headline outcome of this calculation. It is most useful when read alongside the supporting metrics rather than in isolation.
Interest Earned
Growth separated from original capital so you can compare savings or investment scenarios on an equal footing. Tax treatment depends on the account and jurisdiction.
Method & assumptionsAuthoritative sources
This calculator uses the standard compound interest formula: A = P(1 + r/n)^(nt), where P is your principal, r is the annual interest rate expressed as a decimal, n is the number of compounding periods per year, and t is the number of years. It assumes a constant interest rate throughout, which is rarely guaranteed in practice — savings rates change, and investment returns fluctuate. The results are nominal figures and do not account for inflation, tax, or product charges. UK savers should note that the AER figure on savings products already standardises for compounding frequency, making it the fairest basis for comparison. This tool is for illustrative purposes only and does not constitute financial advice.
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.
Go deeper — 4 guides reference this calculator
UK Mortgage Overpayments Guide: When to Clear Faster and When to Save Cash
How 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 Next
A 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 Pension Allowances 2026/27: Annual Allowance, Taper, Carry-Forward
UK pension contribution limits — £60k annual allowance, tapering for high earners, carry-forward rules, and what changed when the Lifetime Allowance was abolished.
UK ISA Guide 2026/27: Types, £20,000 Allowance, Transfers, LISA
UK Individual Savings Account guide — Cash, Stocks & Shares, Lifetime and Innovative Finance ISAs, the £20,000 allowance, transfer rules and the 25% LISA bonus.
Frequently asked
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