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Compound Interest Calculator

Calculate how compound interest grows savings or increases debt over time. Enter principal, rate, compounding frequency and term to project your final balance.

Last reviewed 15 August 2026

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When to use this calculator

  • Before choosing between saving, investing or changing a contribution.
  • When you want to compare cautious, base and optimistic return assumptions.
  • When you need a projection before making a longer-term decision.
  • When you want to see whether starting earlier or contributing more changes the outcome more.

A realistic South Africa planning example

Use these sample inputs as a quick scenario test, then change one variable at a time to compare outcomes.

A realistic South Africa planning example
InputValue
Initial Amount (R)R15,000
Annual Interest Rate (%)5%
Years10 years
Compounds Per YearAnnually (1x/year)

After entering these figures, review total and interest earned together rather than in isolation. Then rerun the tool with one input adjusted.

How to read your results

Total

The headline outcome of this calculation. It is most useful when read alongside the supporting metrics rather than in isolation.

Interest Earned

Growth separated from original capital so you can compare savings or investment scenarios on an equal footing. Tax treatment depends on the account and jurisdiction.

Common mistakes

  • !Using an assumption that is not supported by a current local quote, bill, statement or official source.
  • !Treating a generic estimate as a lender, provider, payroll or tax authority decision.
  • !Mixing monthly and annual inputs without converting them consistently.
  • !Testing only one scenario instead of checking how a cautious assumption changes the result.

What to do next

  • Run a second scenario with a cautious assumption so you can see the downside clearly.
  • Compare the result with the related calculators below before making a decision.
  • Check current local rules, eligibility and provider terms before applying or committing money.
  • Keep a record of the assumptions so you can update the estimate when a quote, bill or pay figure changes.

Frequently asked

The compound interest calculator applies your interest rate compounded at regular intervals (daily, monthly, quarterly, or annually) over your investment period. Interest earned is added to principal, then earns interest itself, creating exponential growth.

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