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Compound interest / APY calculator

Project an ending balance from a starting amount, rate, compounding schedule, and optional contributions. Math is deterministic TypeScript — not advice, not a forecast, and not a recommendation.

Starting amount and rate
Rate type
Term and compounding
Optional recurring contribution
Contribution timing

Results

Ending balance
$31,998.32
Total contributions
$22,000.00
Interest earned
$9,998.32
Effective APY
5.1162%

Assumptions

  • Periodic rate i = r / n for nominal annual rate r compounded n times/year.
  • Future value without contributions: PV (1 + i)^(n t).
  • With end-of-period contributions PMT: PV (1 + i)^(n t) + PMT ((1 + i)^(n t) − 1) / i.
  • Beginning-of-period contributions multiply the annuity factor by (1 + i).
  • APY from nominal: (1 + r / n)^n − 1.
  • Daily compounding uses n = 365 (no leap-day adjustment).
  • When contribution frequency differs from compounding, each compounding period receives contribution × (contributions-per-year / compounds-per-year).
  • Displayed currency amounts round to the nearest cent (half away from zero).
  • Empty or invalid inputs produce no result.

Related Learn reading stays on published guides only. Browse the Learn library for bonds, yields, and market mechanics. Dedicated APY and compounding notes will link here when they are live.

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