Accrued Loan Interest: How It Builds and Is Calculated

Accrued loan interest is the interest that has built up on a loan over time but has not yet been paid. This calculator estimates interest accrued on a simple-interest loan from its balance, annual rate, and elapsed days; enter those figures to see the estimated interest and balance including it.

Formula

The calculator uses a simple-interest estimate, with a 365-day year:

• Accrued interest = principal × annual rate × elapsed days ÷ 365.
• Balance including accrued interest = principal + accrued interest.

Here, p is the loan balance in dollars, apr is the annual interest rate entered as a percentage, and d is the number of days. The rate is divided by 100 to convert the percentage to a decimal. The result is rounded to the nearest cent. This is an estimate under the stated convention, not a substitute for a lender’s precise daily calculation.

Worked Example

Using the default inputs—$20,000, an 8% annual rate, and 30 days:

1. Convert the annual rate to a decimal: 8 ÷ 100 = 0.08.
2. Multiply balance by rate and days, then divide by 365: $20,000 × 0.08 × 30 ÷ 365 = $131.5068….
3. Round to cents: accrued interest = $131.51.
4. Add it to the starting balance: $20,000 + $131.51 = $20,131.51.

What Accrued Loan Interest Means

Interest is the cost of borrowing money, generally calculated against an outstanding principal balance. It accrues as time passes. “Accrued” describes interest that has accumulated during a period, whether or not a payment is due or has been made yet. The exact amount depends on the loan’s terms and how the lender counts days, applies payments, and handles compounding.

Accrued interest is not necessarily an extra fee. It is interest under the loan agreement. It may be paid as part of a scheduled installment, settled when a balance is paid off, or treated in another way specified by the contract. It is also distinct from the principal: principal is the borrowed amount still owed, while interest is the borrowing cost that accumulates.

How Accrual Works Between Payments

For a simple-interest loan, interest may be calculated daily on the current principal. A simplified daily calculation is principal × annual rate ÷ 365; multiply that daily amount by the number of days to estimate the accrual. For example, at 8% on a constant $20,000 balance, the simplified daily amount is about $4.38. Over 30 days, that is about $131.51.

Actual balances can change during the period. If a payment reduces principal, later daily interest may be calculated on the lower balance. Some products instead use another day-count convention, such as a 360-day year, or apply compounding under their terms. A lender’s statement or payoff figure can therefore differ from this calculator even when the starting balance and stated rate match.

Accrued interest can also exist when no payment is currently due. Whether it is paid, capitalized (added to principal), or handled differently depends on the contract and applicable account rules. Capitalization changes the amount on which future interest may be calculated; it is not the same as merely recording unpaid interest.

When This Estimate Is Useful

This calculation can help explain how elapsed time affects a balance, make a rough comparison of accrual over different day counts, or check the scale of a simple-interest estimate. It can be useful for understanding a statement or preparing questions for a loan servicer. For a real payoff, payment, or accounting figure, use the lender’s quoted amount and the loan documents’ calculation method.

Enter the balance on which interest is accruing—not necessarily the original amount borrowed—and the rate that applies to that balance. Enter elapsed days for the period being estimated. The calculator assumes the balance and rate stay constant throughout those days. If payments, rate changes, fees, or capitalization occurred during the period, one single calculation will not represent the full account history.

Common Sources of Differences

• Day-count convention: A 360-day basis produces a different daily amount than a 365-day basis. Leap-year or contract-specific treatment can matter too.
• Changing principal: Payments and other adjustments can change the balance used to calculate later interest.
• Compounding: Simple interest is calculated on principal in this estimate. With compounding, unpaid interest may affect later interest calculations according to the agreement.
• Dates and rounding: The start date, end date, posting date, and rounding at each step can affect cents. The calculator rounds its final interest result to cents.
• Rate type: A variable rate may change during the period. Using one annual rate throughout cannot capture that change.

A frequent misconception is that accrued interest always means interest has been added to the loan principal. It does not: accrual means it has built up. Whether unpaid interest is capitalized is a separate question governed by the loan’s terms. Another point to check is whether a quoted annual rate is the rate used for accrual or a broader disclosure measure that includes other costs; those figures are not interchangeable in every context.

Frequently Asked Questions

Is accrued interest the same as unpaid interest?
Not always in usage. Accrued interest is interest accumulated over a period; it may remain unpaid, or it may be included in a payment. Check the statement and loan terms to see how it is recorded.

Does accrued interest increase the loan principal?
Not automatically. It increases the amount owed in an economic sense, but it becomes part of principal only if it is capitalized under the loan’s terms.

How do I calculate accrued interest for a loan?
For a simple estimate, multiply the balance by the annual rate as a decimal and by the fraction of a year elapsed. This calculator uses days ÷ 365 as that fraction; a lender may use a different convention.

Why is my lender’s accrued interest different?
The lender may use a different day-count basis, dates, balance, rounding method, or compounding treatment. Payments or rate changes during the period can also account for the difference.

Is accrued interest included in a payoff amount?
A payoff quote commonly accounts for amounts due through a specified date, but its calculation depends on the loan and quote terms. Ask the lender for a dated payoff figure rather than relying on this estimate.

Assumptions and Limits

• The balance and annual rate are constant across the entered period.
• Interest is estimated as simple interest on the entered balance.
• A 365-day year is used; daily compounding and payment activity are not modelled.
• Fees, taxes, insurance, and other account charges are excluded.

This calculation is educational estimate arithmetic, not financial advice. The result is an estimate, and the lender’s disclosure gives the exact figures.

Related

• Borrowing Against Equity: How It Works
• Home Equity Borrowing Options: How They Compare
• Home Equity Borrowing Process: Steps and Costs

in p | Loan balance | $ | 20000 | 0 | 100000000
in apr | Annual interest rate | % | 8 | 0 | 100
in d | Days accrued | days | 30 | 0 | 36500
out int | Accrued interest | $ | p * (apr / 100) * d / 365 | 2
out bal | Balance including accrued interest | $ | p + int | 2