Accrued Interest Calculator: How It Works

Accrued interest is interest that has built up over time but has not yet been paid or posted to an account. This calculator estimates it from a balance, annual interest rate, and number of days, using simple daily accrual; it returns the interest earned or owed for that period.

Formula

The estimate uses simple interest prorated by the number of days: accrued interest = balance × (annual rate ÷ 100) × days ÷ 365. In symbols, I = P × (r ÷ 100) × d ÷ 365.

• I is accrued interest, in dollars.
• P is the principal or balance on which interest accrues, in dollars.
• r is the annual interest rate entered as a percentage.
• d is the number of days in the accrual period.

The second result, P + I, is the balance plus this period’s estimated interest, before any payment, fee, new borrowing, or other adjustment. The calculator uses a 365-day denominator as a simplifying assumption. Some contracts or financial products use a different day-count convention, such as 360 days, actual calendar days in the year, or a schedule that compounds interest. Check the relevant statement or contract for its method.

Worked Example

Using the calculator’s default inputs—$20,000 balance, 8% annual rate, and 30 days—the steps are:

1. Convert the percentage to a decimal: 8 ÷ 100 = 0.08.
2. Calculate one year’s simple interest: $20,000 × 0.08 = $1,600.
3. Prorate for 30 days using 365 days: $1,600 × 30 ÷ 365 = $131.5068…
4. Round to cents: accrued interest is $131.51.
5. Add it to the starting balance: $20,000 + $131.51 = $20,131.51.

This is an estimate under the stated assumptions, not necessarily the amount a lender or account provider will post. Their calculation may use a different daily balance, day-count basis, or compounding schedule.

What Accrued Interest Means

Interest is generally the cost of borrowing money or the return paid for allowing money to be used. It accrues as time passes. “Accrued” describes interest that has accumulated economically, even if the payment date has not arrived or the amount has not yet appeared as a separate line on a statement.

For a borrower, accrued interest may be an amount owed in addition to principal. For a saver or investor, it may be income earned but not yet paid. The exact accounting and timing depend on the product and its terms. Accrued interest is not always the same as interest that has been billed, paid, capitalized into principal, or received in cash.

How Daily Accrual Works

With simple daily accrual and a constant balance, each day adds roughly the same amount of interest. At $20,000 and 8% on a 365-day basis, the daily amount is $20,000 × 0.08 ÷ 365, or about $4.38. Thirty days therefore produce about $131.51 before rounding.

In practice, some balances change during the period. A credit card balance, for example, can shift with purchases, payments, credits, and fees. A calculation based only on the starting balance will not reproduce a method that applies a daily rate to each day’s changing balance. Similarly, if interest is compounded, previously accrued interest may itself begin earning interest. This calculator does not model either a changing daily balance or compounding.

For an account with multiple transactions, an estimate may require the balance for every day—or the product’s specified average daily balance method—rather than one opening balance. Use the provider’s stated calculation method when reconciling a statement.

Where It Appears and Why It Matters

• Loans: Interest can accumulate between payment dates. A payoff figure may include interest through a specified date, so it can differ from the displayed principal balance.
• Credit cards: Interest may depend on daily balances and payment timing. A simple estimate using one balance cannot account for all transaction dates or product-specific terms.
• Bonds and other investments: Interest may accumulate between scheduled payment dates. In some transactions, the buyer may compensate the seller for interest earned since the last payment; the instrument’s terms determine the treatment.
• Savings and deposit accounts: Interest can accrue before it is credited or paid. The posting schedule and calculation basis are set by the account terms.

Accrued interest can help explain why an amount due is not identical to the original principal or why a statement balance changes over time. It is also useful for checking a rough estimate, provided the balance, rate, period, and day-count method match the product.

Common Misunderstandings and Limits

• Accrued interest is not necessarily compounding. Accrual is the buildup of interest; compounding is the process of adding interest to the balance on which future interest is calculated.
• It is not always the same as the next payment’s interest portion. Payments can cover interest and principal according to a schedule, while accrued interest may be measured for a different date range.
• The annual rate alone does not determine the exact amount. The applicable balance, dates, day-count basis, rounding, and contract terms matter.
• A zero-day period gives zero in this formula. A negative number of days is not accepted because elapsed time for this estimate cannot be negative.

For a more precise reconciliation, identify whether the stated rate is nominal or effective, whether the balance changes during the period, how many days count, and whether accrued interest compounds. Do not treat this simplified result as a payoff quote or an account statement.

Assumptions

• The balance stays constant throughout the selected period.
• The entered annual percentage rate is applied as a simple annual rate, prorated evenly by day.
• The year is treated as 365 days, including for periods that cross a leap day.
• Interest is not compounded, and no payments, deposits, fees, taxes, or other balance changes are included.
• Amounts are rounded to cents for display; a provider may retain more precision during its calculation.

Frequently Asked Questions

Is accrued interest paid or unpaid?
It has accumulated, but whether it has been paid depends on the timing and terms of the account. It may be unpaid until a scheduled payment or crediting date.

How do I calculate accrued interest per day?
For simple daily interest, divide the balance multiplied by the annual rate as a decimal by the number of days in the year. With $20,000 at 8% on a 365-day basis, that is about $4.38 per day.

Does accrued interest increase the principal?
Not automatically. It increases principal only when the applicable terms or accounting process capitalize it. Accrued interest can remain separately tracked until payment or posting.

Why does my statement show a different amount?
The provider may use a changing daily balance, a different day-count convention, compounding, transaction-specific dates, or a different rounding rule. Compare the method and dates used before drawing conclusions.

Is accrued interest the same as APR?
No. APR is a rate expressed annually; accrued interest is a dollar amount accumulated over a particular period. This calculator uses the entered annual rate to estimate that amount.

This result is an estimate for educational purposes; the lender’s disclosure or account terms give the applicable calculation and exact figures.

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in bal | Balance | $ | 20000 | 0 | 100000000
in apr | Annual interest rate (APR) | % | 8 | 0.01 | 100
in days | Days accrued | days | 30 | 0 | 3650
out int | Accrued interest | $ | bal * (apr / 100) * days / 365 | 2
out total | Balance plus accrued interest | $ | bal + int | 2