Compound Interest Calculator
See how your savings grow over time with compound interest.
Compound interest inputs
Enter your starting balance, contribution, rate, and time horizon.
Currency
Starting amount invested or saved.
Recurring deposit made at the selected frequency.
Expected annual return before taxes, fees, and inflation.
How long the money compounds (0-100 years, fractional values allowed).
How often interest is added to the balance.
How often the regular contribution is added.
Annual contribution
£3,000.00
Monthly equivalent
£250.00
Rate per compound period
0.58%
Final balance
£170,619.05
After 20 years at 7.00%.
Interest earned
£100,619.05
58.97% of final balance.
Total invested
£70,000.00
Initial principal plus total contributions.
Total contributions
£60,000.00
Monthly contributions over the term.
Principal future value
£40,387.39
Future value of the starting principal.
Contribution future value
£130,231.66
Future value created by recurring deposits.
Growth multiple
2.44×
Final balance divided by total invested.
Contribution share
76.33%
Share of final balance from recurring deposits.
Export
Save or share this growth estimate
Copy the summary, download a CSV version, or print a compact projection summary.
Growth breakdown
What makes up the final balance
Starting principal
£10,000.00
Initial amount
Total contributions
£60,000.00
Deposits added
Interest earned
£100,619.05
Estimated growth
Yearly projection
Year-by-year compound growth
See how contributions and estimated interest build the balance over time.
| Year | Opening balance | Contributions | Interest | Closing balance |
|---|---|---|---|---|
| Year 1 | £10,000.00 | £3,000.00 | £821.05 | £13,821.05 |
| Year 2 | £13,821.05 | £3,000.00 | £1,097.27 | £17,918.32 |
| Year 3 | £17,918.32 | £3,000.00 | £1,393.46 | £22,311.78 |
| Year 4 | £22,311.78 | £3,000.00 | £1,711.07 | £27,022.85 |
| Year 5 | £27,022.85 | £3,000.00 | £2,051.63 | £32,074.48 |
| Year 6 | £32,074.48 | £3,000.00 | £2,416.81 | £37,491.29 |
| Year 7 | £37,491.29 | £3,000.00 | £2,808.39 | £43,299.69 |
| Year 8 | £43,299.69 | £3,000.00 | £3,228.28 | £49,527.97 |
| Year 9 | £49,527.97 | £3,000.00 | £3,678.53 | £56,206.50 |
| Year 10 | £56,206.50 | £3,000.00 | £4,161.32 | £63,367.82 |
The yearly table is an estimate based on the selected compounding and contribution frequencies. Real account timing, fees, taxes, and investment changes can alter results.
Interpretation
What these compound interest results mean
Future value estimate
Your balance could grow to about £170,619.05 after 20 years based on your inputs.
Interest earned
Estimated interest is £100,619.05, which is the difference between final balance and total invested.
Contribution effect
Your recurring deposits add £60,000.00 before growth, and their future value is estimated at £130,231.66.
Time horizon
If the same assumptions continued for 5 more years, the balance could project to about £259,772.11.
Compound interest basics
How compound interest works
Principal
Principal is the starting amount that begins earning interest.
Interest rate
The annual rate controls how quickly the balance grows before taxes, fees, and inflation.
Compounding
Interest is added back into the balance, allowing future interest to build on earlier interest.
Contributions
Regular contributions can become a major part of long-term savings growth.
Formula
Compound interest formula explanation
Compound interest
A = P(1 + r/n)^(nt)A is final amount, P is principal, r is annual rate, n is compounding periods per year, and t is time in years.
Interest earned
Interest = Final Balance − Total InvestedInterest earned separates growth from the money originally invested or contributed.
Growth multiple
Growth Multiple = Final Balance ÷ Total InvestedGrowth multiple shows how many times the invested money became after compounding.
Growth drivers
What affects compound growth
Time
Longer time horizons give interest and contributions more years to compound.
Return rate
Higher assumed rates can increase future value, but may involve higher risk for investments.
Contribution habit
Regular contributions can matter more than small differences in compounding frequency.
Frequency
More frequent compounding can help, though the effect may be modest compared with rate and time.
Inflation
Inflation can reduce the purchasing power of the future balance.
Taxes and fees
Taxes and account fees can reduce real-world returns.
Comparison
Compound interest vs simple interest
Without contributions
£40,387.39
The starting principal alone would grow to this amount with the selected rate and compounding frequency.
With contributions
£170,619.05
Regular contributions increase the projected balance and give more money time to compound.
Use cases
Common compound interest calculator use cases
Savings goals
Estimate how regular deposits can grow toward a future savings target.
Retirement planning
Model long-term contributions and growth over many years.
Investment projections
Test different return assumptions for a portfolio or fund.
Education savings
Estimate how savings could grow before future education costs.
Emergency fund growth
See how interest can add to cash reserves over time.
Long-term wealth building
Understand how starting early can affect future balances.
Trust
About this estimate
Transparent method
Uses compound interest math plus recurring contribution growth to estimate future value.
Real-world limits
Results are nominal estimates and do not include taxes, fees, inflation, market volatility, or account limits.
Planning focused
Compare starting balances, contribution habits, time horizons, return assumptions, and compounding frequency.
FAQ
Compound interest calculator questions
Compound interest is interest earned on both the original principal and previously earned interest. Over time, this creates interest on interest.
The standard formula is A = P(1 + r/n)^(nt). P is principal, r is annual rate, n is compounding periods per year, and t is time in years.
Each contribution is added at the end of its contribution period (for example, at the end of each month for monthly contributions) and then grows at the selected compounding rate from its own contribution date until the end of the term. A contribution made on the very last day of the term is counted in the total but has no time left to earn interest.
Simple interest is calculated only on the original principal. Compound interest is calculated on principal plus accumulated interest.
More frequent compounding can slightly increase returns, but the annual rate, contribution amount, and time horizon usually have a larger impact.
Yes. More frequent contributions give money more time to compound. Contribution amount and consistency often matter more than small differences in compounding frequency.
It depends on the account or investment. Savings accounts may use lower rates, while long-term investments may use higher assumptions with more risk.
No. It estimates nominal growth before taxes, account fees, inflation, and market volatility.
No. This calculator is for educational estimates only. Real returns can vary and investments can lose value.
Estimate only. This calculator is for general planning and education, not financial, tax, investment, legal, lender, or professional advice. Compounding examples are estimates. Actual rates, terms, fees, taxes, and withdrawal rules can vary by account or provider. Verify important decisions with a qualified professional, lender, official source, or relevant institution.
Related reading
Learn the formula, assumptions, examples, or context behind this tool.