Contributions versus growth
How much final value comes from deposits and how much comes from estimated returns.
ContributionsGrowth
Compound Growth Calculator
Project savings or investment growth with monthly contributions, annual returns, and contribution increases.
Projected value£249,075After 20 years
Contributions£126,627Including starting balance
Growth£122,448Estimated compound return
Projected balance
The full balance path through the selected period.
Balance
Final value split
Final value split before any optional tax estimate.
Amount
Growth breakdown
Starting balance£10,000
Final monthly contribution£583
Growth share49.2%
Assumed annual return6.0%
Tax estimate
ModeNo CGT estimate
Rules year6 April 2026 to 5 April 20272026/27
Capital gain modelled£122,448
CGT annual exempt amount£3,000
Estimated CGTNot applied£0
Assumptions
Calculation notes
- Uses monthly compounding and a constant return assumption.
- Tax estimate is off by default; ISA and pension wrappers have different tax treatment.
- Does not include fees, inflation, platform charges, or market volatility.
- Negative return assumptions are allowed for stress testing.
Growth scenario
How compounding changes the projection
The projection separates contributions from assumed growth so the result can be stress-tested.
Compounding method
The calculator projects the opening amount forward using the selected contribution pattern and assumed annual growth rate.
It separates money paid in from estimated growth so the result is easier to interpret, and optional tax assumptions can be modelled where the tool supports them.
Growth pathopening balance + regular contributions + compound growth - optional tax adjustment -> projected value
Monthly contribution example
Example: GBP 10,000 plus GBP 250 per month
- Starting amount: GBP 10,000
- Monthly contribution: GBP 250
- Term: 5 years
- Assumed growth: 5% a year
Result: The projected balance is roughly GBP 29,700 before any tax adjustment, with about GBP 4,700 coming from estimated growth.
Most of the value over a short period still comes from contributions, while longer periods make the growth assumption much more important.
Scenario sensitivity
- Small changes in assumed return can make a large difference over long periods, so use scenarios rather than treating one projection as certain.
- The projection does not guarantee investment performance and does not model every possible fee, tax wrapper or platform charge.
Content reviewed: 7 September 2026.
Guide
Compound Growth Calculator notes
Explore how starting balance, monthly saving, annual return, and contribution step-ups affect long-term growth.
Choose the rules year that matches the scenario you are checking.
Review the calculation notes where rules, tax years, thresholds, or eligibility affect the result.
FAQs
Compound Growth Calculator FAQs
What is the Compound Growth Calculator for?
Explore how starting balance, monthly saving, annual return, and contribution step-ups affect long-term growth.