Accrued Interest Calculator and How It Works

Accrued interest is interest that has built up on a loan or investment over time but has not yet been paid or credited. This calculator estimates simple accrued interest when you enter the principal, annual interest rate, and elapsed time; it returns the interest and the principal-plus-interest amount.

Formula

This calculator uses simple interest on an actual-days/365 basis:

Accrued interest = principal × annual rate × days accrued ÷ 365

• Principal (p): the amount on which interest is calculated, in dollars.
• Annual interest rate (apr): the yearly rate entered as a percentage. The formula converts it to a decimal by dividing by 100.
• Days accrued: elapsed days in the accrual period.
• Accrued interest (int): unpaid interest accumulated during those days, in dollars.
• Principal plus accrued interest (total): the principal plus this period’s calculated interest, in dollars; it does not include other charges or earlier unpaid interest.

The 365-day denominator is an assumption, not a universal convention. Some contracts and securities use a 360-day year, actual days in the calendar year, or another specified day-count method. Use the convention applicable to the account or instrument when you need a contract-level figure.

Worked Example

Using the calculator’s defaults—$20,000 principal, an 8% annual rate, and 30 days—the steps are:

1. Convert the rate to decimal form: 8 ÷ 100 = 0.08.
2. Multiply principal by the rate: $20,000 × 0.08 = $1,600 per year.
3. Apply the time fraction: $1,600 × 30 ÷ 365 = $131.5068…
4. Round accrued interest to cents: $131.51.
5. Add it to principal: $20,000 + $131.51 = $20,131.51.

Assumptions

• The rate remains fixed for the entered accrual period.
• Interest accrues evenly each day, without intermediate payments.
• The calculation uses simple interest and a 365-day year; it does not compound interest daily or monthly.
• Fees, taxes, payment timing, changing balances, and contract-specific day-count rules are not included.

What Accrued Interest Means

“Accrued” describes interest earned or owed as time passes, whether or not a payment has happened yet. On a loan, it can be an amount the borrower owes in addition to principal. On an interest-bearing deposit or bond, it can be earnings that have accumulated but have not yet been paid out. The direction of the payment differs, but the underlying idea is the same: interest is associated with a period of time.

Accrued interest is not necessarily the same as the amount due today. A loan payment may cover some interest and some principal, and the lender’s account calculation may include payment dates, compounding, fees, or a particular day-count convention. Likewise, an investment’s accrued amount may be settled only on a scheduled payment date or when it is sold.

How It Builds Up

With simple interest and an unchanged balance, accrued interest grows in proportion to the principal, rate, and elapsed time. For example, keeping the other inputs fixed, twice as many accrual days produces twice the interest under this calculator’s formula. A larger balance or rate also produces a larger result.

Many real accounts do not stay at a fixed principal. When a borrower makes payments, the outstanding balance may fall; interest after that payment is then calculated on the lower balance, according to the contract. If unpaid interest is added to the balance and future interest is charged on that larger amount, the calculation involves compounding. This simple calculator does not model either changing balances or compounding.

For a quick estimate over part of a year, the time fraction is days ÷ 365. For a full year at 8% on $20,000, simple interest would be $1,600. For 30 days, the result is about $131.51—not $1,600—because only 30/365 of a year has elapsed under the stated assumption.

When the Estimate Is Useful—and Its Limits

This calculation can help explain why interest appears between regular statement or payment dates, estimate simple interest for a short period, or check the basic arithmetic behind an accrual. It is also useful for separating the idea of accumulated interest from a scheduled payment: the figure is an estimate of interest over the entered period, not a payment schedule.

For an exact payoff, statement balance, bond settlement, or account credit, use the amount and method supplied by the relevant institution or contract. The actual calculation can depend on the balance on each day, when payments post, whether interest compounds, leap years, and the prescribed day-count basis. Rounding at different stages can also create a small difference. Enter the applicable rate and number of days, and do not treat the output as a quote or official balance.

Common Confusion: Accrued vs. Capitalized Interest

Accrued interest has accumulated, but it may remain a separate unpaid amount. Capitalized interest is unpaid interest that is added to the principal or account balance under the applicable terms. Once added, future interest may be calculated on that larger balance if the product compounds. Accrual alone does not prove that interest has been capitalized, and capitalization does not happen merely because a calculator displays an accrued amount.

Another frequent misunderstanding is assuming that “annual rate” always means the same daily calculation. The rate and the day-count convention work together. A rate stated per year does not, by itself, reveal whether the calculation uses 365, 360, or another basis. Check the account documents for that detail.

Frequently Asked Questions

How do you calculate accrued interest?
For simple interest, multiply principal by the annual rate as a decimal and by the fraction of a year elapsed. This calculator uses days ÷ 365 for that fraction.

Is accrued interest the same as interest due?
Not always. Accrued interest is the interest accumulated over a period. The amount currently payable can depend on the payment schedule, account terms, previous payments, and other charges.

Does accrued interest compound?
Not automatically. Simple accrued interest does not itself include interest on prior interest. Compounding applies when the product’s terms add interest to the balance or otherwise calculate interest on accumulated interest.

Why does my lender’s figure differ from this calculator?
The lender may use a different day-count basis, daily balance, compounding method, payment-posting date, or rounding process. This tool assumes a fixed balance, simple interest, and a 365-day year.

What does accrued interest mean on a bond?
It generally refers to interest accumulated since the last interest payment date. The precise amount and how it is settled depend on the bond’s terms and applicable calculation convention.

This result is an estimate; the lender’s disclosure gives the exact figures.

Related

• Accrued Interest on FD: Journal Entry and Examples
• NSC Accrued Interest Calculator and Explanation
• Accrued Interest Calculator: Meaning and Formula

in p | Principal | $ | 20000 | 0 | 100000000
in apr | Annual interest rate | % | 8 | 0.01 | 100
in days | Days accrued | days | 30 | 0 | 36500
out int | Accrued interest | $ | p * (apr / 100) * days / 365 | 2
out total | Principal plus accrued interest | $ | p + int | 2