Simple interest (days)

Reverse solve elapsed days from principal, future value, and rate.

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Calculation specification

Reviewed on:

Formula basis

days=(FV/PV−1)×d/(rate/100), where d is 365, 360, 30, or 1.

Calculation method

Derives the elapsed time required to move from principal to future value at a simple rate and selected basis.

Exclusions and checks required

  • Zero rate or a target direction inconsistent with the rate cannot produce a valid duration.
  • Fractional days are not converted to calendar dates; holidays, start-date rules, tax, and fees are excluded.

Example input:：Days for JPY 1 million to become JPY 1.1 million at 5%

simpleMode
365
simpleRate
5
principal
1000000
futureValue
1100000

The output is a mathematical fractional day count, not a contractual date.

FAQ

Who is this calculator for? Simple interest (days)

Reverse solve elapsed days from principal, future value, and rate.

What values should I enter?

Applies to: Simple interest / days = (FV/PV − 1) × basis ÷ r

How should I interpret this estimate?

Derives the elapsed time required to move from principal to future value at a simple rate and selected basis.

How to use

  1. Enter your input values and press Calculate.
  2. Review the result and compare it with expected context.
  3. days=(FV/PV−1)×d/(rate/100), where d is 365, 360, 30, or 1.