Compound Interest Calculator

Compound interest calculator for monthly savings growth

This compound interest calculator helps you see how a once off starting amount and regular monthly contributions can grow over time at a fixed annual interest rate. It is useful for retirement planning, education savings and any medium to long term goal.

Enter your current balance, how much you can add every month, the interest rate you expect and how many years you want to invest for. The calculator shows your future balance, how much of that comes from your own contributions and how much is pure interest growth.

Results are shown using monthly compounding. This matches the way many savings accounts, unit trusts and investment products work in practice, where interest is added to your balance each month.

Assumptions and how to use this calculator

• The interest rate is fixed for the full period and does not change from year to year.
• Interest compounds monthly, and monthly contributions are added at the end of each month.
• No tax, fees or transaction costs are deducted from the investment growth.
• The annual interest rate is entered as a simple percentage, for example 8 for 8 percent.
• The calculator is for planning and illustration and is not financial advice.

Common questions about this calculator

What is compound interest?

Compound interest is interest that earns interest. Instead of paying interest only on your original amount, the bank or investment provider calculates interest on both your starting balance and all past interest that has been added. Over time this can lead to strong growth.

Why does the calculator use monthly compounding?

Many savings and investment products credit interest monthly, and most people contribute monthly as well. Using monthly compounding keeps the maths aligned with how real accounts work and gives a realistic picture of your possible future balance.

What happens if my interest rate is zero?

If you enter an interest rate of zero, the calculator simply adds your starting amount and all monthly contributions without any growth. This is useful if you want to compare saving in cash with investing at a positive interest rate.

Can I use this for debt calculations?

This calculator is designed for savings and investments where you deposit money. For loans and credit where you repay a balance, it is better to use a loan repayment or amortisation calculator that focuses on instalments and outstanding debt.

How accurate are the results?

The formulas use standard compound interest maths and are accurate for the assumptions listed above. Real world returns can differ if your rate changes over time, if fees are charged or if contributions are skipped or varied.