Estimate how your savings or investments grow over time using compound interest. This calculator helps you understand how interest builds on both your initial deposit and ongoing contributions.
✔ Compound interest • ✔ Investment growth • ✔ Savings projection • ✔ Free calculator
Our Compound Interest Calculator estimates how savings and investments can grow over time using the power of compound interest. Whether you are saving for retirement, building an emergency fund, investing through a Stocks and Shares ISA, or planning long-term wealth, this calculator provides an estimate of your future investment value based on your starting balance, annual return, investment period, and optional monthly contributions.
Unlike many basic compound interest calculators, this tool also estimates the total amount invested, interest earned, investment growth, inflation-adjusted value, and provides a year-by-year breakdown to help you understand how your money grows over time.
Compound interest is the process of earning interest not only on your original investment but also on the interest that has already accumulated. Because each year's earnings become part of your investment balance, future returns are calculated on an increasingly larger amount.
This is why compound interest is often called "interest on interest". The longer your money remains invested, the more powerful this effect becomes.
The basic compound interest formula is:
A = P × (1 + r / n)nt
When monthly contributions are added, the calculation becomes more advanced because every contribution earns compound interest for a different length of time.
When interest is added to your account, it becomes part of your balance. Future interest calculations are then based on the larger amount.
The longer your money remains invested, the greater the effect of compounding becomes.
Small differences in interest rates can produce significant differences in final results over long periods.
After 10 years, the investment would grow to approximately £1,629 if interest is compounded annually.
Regular monthly contributions can dramatically increase the final balance because each contribution has additional time to earn compound interest.
This type of long-term investing demonstrates why compound growth is often described as one of the most effective wealth-building tools available.
The examples below illustrate how different starting balances, contribution amounts, investment periods, and annual returns can affect long-term investment growth. Actual results will vary depending on investment performance, fees, taxes, and the frequency of compounding.
| Initial Investment | Monthly Contribution | Annual Return | Years | Estimated Future Value |
|---|---|---|---|---|
| £1,000 | £0 | 5% | 10 | ~£1,629 |
| £5,000 | £100 | 5% | 20 | ~£48,400 |
| £10,000 | £200 | 7% | 30 | ~£299,000 |
| £20,000 | £500 | 8% | 25 | ~£555,000 |
These examples highlight two important principles of compound interest:
Compound interest is commonly used when estimating the future value of:
Time is one of the most important factors in compound growth.
| Years Invested | Effect of Compounding |
|---|---|
| 5 Years | Modest growth |
| 10 Years | Noticeable growth |
| 20 Years | Significant growth |
| 30+ Years | Powerful long-term growth |
Starting earlier often has a greater impact than investing larger amounts later in life.
Even small increases in annual return can have a large impact over several decades.
| Compound Interest | Simple Interest |
|---|---|
| Interest earns additional interest | Interest calculated only on original deposit |
| Growth accelerates over time | Growth remains linear |
| Common for investments and savings | Common for basic interest calculations |
Compound growth works best when investments are allowed to remain invested over long periods.
What is compound interest?
Compound interest means earning interest on both your original investment and previously earned interest.
Why is compound interest important?
It allows savings and investments to grow faster over time because returns are continually reinvested.
Do monthly contributions make a difference?
Yes. Regular contributions can significantly increase long-term growth.
Can this calculator be used for pensions?
Yes. It can be used to estimate pension growth, retirement savings, and long-term investment plans.
Does this calculator include inflation?
No. Results show nominal growth only and do not account for inflation or investment fees.
Are the results guaranteed?
No. Actual investment returns can vary depending on market performance and the financial product used.
Depending on the investment, interest may compound daily, monthly, quarterly or annually.
Yes. Even a difference of 1–2% per year can significantly increase the final balance over several decades.
The Rule of 72 estimates how long it takes an investment to double by dividing 72 by the annual interest rate.
Regular monthly investing generally allows your money to start compounding sooner and can help smooth out market fluctuations.
Whether you are investing for retirement, building long-term wealth, saving for a home deposit, or planning your children's future, understanding compound interest can help you make better financial decisions. Use our Compound Interest Calculator to compare different contribution amounts, investment periods, and interest rates to see how small changes today could make a significant difference over time.
Information on this page is based on publicly available guidance, official government publications, and commonly accepted financial calculation methods.
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Last Updated: August 2026