Accurate Interest Calculator

Simple and Compound Interest Calculations for Savings, Investments or Loans

This calculator calculates the interest amount due between any two dates. In addition to simple interest is supports a dozen compounding periods (did we miss any? :). You can also enter negative interest rates.

Because this calculator is date sensitive, it is a suitable tool for calculating the interest owed on a debt. You can use it to calculate accrued interest from any point when the balance is known. More details below the calculator

Related: If you need to calculate interest for a series of payments, investments (deposits) or withdrawals, then you should use this Future Value of an Annuity Calculator.


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Compound Interest

Compound interest means that interest gets paid (or is earned) on previously unpaid interest.

Date selection via pop-up calendar

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For example, if the interest rate is 2% and you start with $1,000 after the end of a year, you'll earn or owe $20 in interest (using annual compounding). Then at the end of two years, assuming there have been no withdrawals (or payments) you earn $20.40, not $20. The previous period's interest earned interest as well.

This pattern is called compounding, and it repeats as long as the money stays invested, or the debtor owes on the debt.

If you are an investor, you want to compound interest. If you are a debtor, you want to avoid it, particularly if you ever miss a payment or a payment is not enough to cover the interest due.

Simple Interest

Per Dictionary.com simple interest is "interest payable only on the principal." Interest is never earned or collected on previous interest.

Using the above example, if the interest rate is 2% and you start with $1,000 after the end of a year, you'll earn or owe $20 in interest. Then at the end of two years, assuming there have been no withdrawals (or payments) you earn another $20.00, (not $20.40). The previous period's interest does NOT earn interest.

Other details

You may select 360, 365, or 366 days in a year. The "Days In Year" option only impacts the interest calculation for simple interest or when the calculator is set to daily compounding, or when the time between the two dates includes a fractional or stub period. What's a fractional period? A fractional period incorporates the odd days "leftover" that are not numerous enough for another compounding period. If compounding is set to "Monthly" and the dates are set to March 15 and April 20, then there are five odd days and those 5 days create the fractional period (in this case, a fractional month). Fractional periods can lead to some strange results when compounding interest. It is possible for the interest calculation to result in a larger amount for a less frequent compounding frequency than for a more frequent compounding frequency.

You can use this online interest calculator as a:

  • apy calculator
  • daily interest calculator
  • investment interest calculator
  • loan interest calculator
  • negative interest rate calculator
  • savings account interest calculator

As a side benefit to this calculator's date accuracy, you can use it for date math calculations. That is, given two dates, it will calculate the number of days between them, or it will find the date that is "X" days from the first date.

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