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Compound Interest Calculator

UniversalDeterministic arithmeticClass A · deterministic arithmeticNo statutory rules requiredMethodology
AUD
AUD

Enter a rate and timeframe to see the balance grow with compound interest.

Summary

Enter a rate and timeframe to see the working behind the projection.

Working

  1. i = annual rate ÷ periods per year (12 monthly, 4 quarterly, 1 annually)
  2. each period: interest = balance × i, then balance = balance + deposit
  3. interest is rounded half-up to the cent as it is credited
  4. closed form: FV = P × (1 + i)ⁿ + C × ((1 + i)ⁿ − 1) ÷ i, with an extra (1 + i) factor for start-of-period deposits
  5. the simulation and the closed form are compared every time; a mismatch beyond per-period rounding is a failure, not a warning

Assumptions

  • The rate is constant for the whole projection and interest is credited on the stated cycle.
  • Deposits are made in full every period, and nothing is withdrawn.
  • Tax on interest, account fees and inflation are excluded from the nominal figures.

Limitations

  • A projection over many years is an arithmetic illustration, not a prediction: real returns vary and can be negative.
  • Variable-rate accounts, introductory bonus rates and conditions attached to bonus interest are not modelled.
  • No product, provider or rate is being offered or compared here.
  • Result accuracy class A: deterministic arithmetic on the figures you enter.