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Compound Interest Calculator

Project a starting balance and monthly contributions with your chosen interest and compounding assumptions.

Last reviewed

Compound Interest Calculator

Projected balance

£31,998.32

Total contributed£22,000.00
Growth£9,998.32

Reading the result

The entered rate stays unchanged; monthly contributions do not earn interest until after they are added.

How it works

The nominal annual rate is converted to an effective monthly growth factor using the selected compounding frequency. Contributions are added at each month end.

Worked examples

Worked example

Starting balance (£): 10000; Monthly contribution (£): 100; Annual nominal rate (%): 5; Years: 10; Compounding: Monthly

  1. The nominal annual rate is converted to an effective monthly growth factor using the selected compounding frequency. Contributions are added at each month end.
  2. Total contributed: £22,000.00
  3. Growth: £9,998.32

Projected balance: £31,998.32

Assumptions

The result depends on the following. If any of them do not match your situation, treat the figure as indicative only.

  • The entered rate stays unchanged; monthly contributions do not earn interest until after they are added.

What this calculator does not do

  • No taxes or withdrawals. Compounding frequency describes the rate basis; actual account crediting and contribution dates may differ.

Methodology

The nominal annual rate is converted to an effective monthly growth factor using the selected compounding frequency. Contributions are added at each month end.

Inputs are processed locally. Displayed amounts are rounded; the calculation retains precision.

Frequently asked questions

Why does compounding frequency matter?

A nominal rate compounded more often usually produces a higher effective annual return. An AER is already an effective annual rate.

How do I model an AER?

Choose annual compounding and enter the AER. The model derives an equivalent monthly rate for monthly contributions.

Please note: Results are estimates for general information only and are not financial, tax or legal advice. Figures depend on the assumptions listed on each page and on your personal circumstances.