Choose Final amount, Starting principal, Daily interest rate, or Number of days, then enter the three known values. This calculator uses a constant daily rate with daily compounding and no deposits or withdrawals.

Constant daily compounding, with no deposits, withdrawals, fees or daily rounding.

Enter the daily rate, not an annual APR or APY. It must be greater than −100%.

Fractional days use exponential interpolation; actual account terms may differ.

Compound Interest Days Calculator Formula

The following equation is used to calculate the Compound Interest Days.

A = P × (1 + r)d
  • Where A is the final amount ($)
  • P is the principal amount ($)
  • r is the daily interest rate as a decimal (the entered daily percentage divided by 100)
  • d is the number of days

To calculate the final balance, multiply the principal by one plus the daily decimal interest rate raised to the number of days. Interest earned is A − P. Fractional days use exponential interpolation and may not match an account’s crediting terms.

What is a Compound Interest Days Calculator?

Definition:

A Compound Interest Days Calculator allows users to determine how much compound interest accumulates on a principal amount over a specific number of days. Enter the principal balance, a daily percentage rate (not an annual APR or APY), and the elapsed days to estimate the balance, including interest on prior interest. Rates are constant; fees, taxes and account-specific daily rounding are excluded.

How to Use the Compound Interest Days Calculator?

Example Problem:

The following example outlines the steps and information needed to calculate the Compound Interest Days.

First, determine the principal amount. In this example, the principal is $1,000.

Next, determine the daily interest rate. Assume the daily interest rate is 0.5% (0.005).

Then, determine the number of days. In this example, there are 30 days.

Finally, calculate the final amount using the formula above:

A = P * (1 + r)^d

A = 1000 * (1 + 0.005)^30

A ≈ $1,161.40

FAQ

Is daily compounding better than monthly compounding?

For the same positive nominal annual rate, daily compounding produces a slightly higher effective annual yield than monthly compounding. Equal APYs instead describe equal annual yields, regardless of how often interest is compounded.

Does the interest rate remain constant throughout the entire period?

In many cases, yes—but this depends on the terms of your account or investment. Some financial products may have variable rates that change over time. The formula provided here assumes a constant rate over the specified days.

Can I convert an annual interest rate to a daily rate?

For a nominal annual interest rate, use the account’s specified day-count basis, often 365 or 360; check its terms. Dividing an APY by 365 is not the equivalent conversion. With daily compounding over D days per year, the APY-equivalent daily percentage is 100 × [(1 + APY/100)^(1/D) − 1]. Enter the resulting daily percentage in this calculator.