360-Day Loan Payment Calculator: Accrual Explained

A 360-day loan payment calculator estimates scheduled payments using a year of 360 days to accrue interest, rather than a 365- or 366-day calendar year. Enter the loan amount, annual rate, and term to see a standard monthly payment and total interest; the calculator uses a monthly-rate approximation, so it is not a daily-accrual calculation.

Formula

This calculator treats the loan as a level-payment loan with monthly periods. Its payment formula is:

Payment = round(P × r / [1 − (1 + r)⁻ⁿ], 2)

• P is the principal, or starting loan balance, in dollars.
• r is the monthly interest rate as a decimal: APR ÷ 1200 when APR is entered as a percentage per year.
• n is the number of monthly payments: loan term in years × 12.
• Payment is the fixed monthly principal-and-interest amount in dollars, rounded to cents.

Total interest is calculated as the rounded monthly payment multiplied by the number of payments, minus the original principal: Total interest = Payment × n − P. The calculator’s formula does not separately calculate interest for each calendar day. It uses the usual monthly amortization method, with the APR divided by 12.

Worked Example

Using the calculator’s defaults—$20,000 principal, 8% APR, and a five-year term:

1. Convert APR to a monthly decimal rate: 8 ÷ 1200 = 0.0066666667.
2. Find the number of monthly payments: 5 × 12 = 60.
3. Substitute in the payment formula: $20,000 × 0.0066666667 ÷ [1 − (1 + 0.0066666667)⁻⁶⁰].
4. Round the payment to cents: $405.53 per month.
5. Use the rounded payment to estimate total interest: $405.53 × 60 − $20,000 = $4,331.80.

These are formula estimates. A lender’s schedule may differ if it calculates interest from actual dates, rounds interest at each payment, or uses other contract terms.

Assumptions

• The interest rate remains fixed for the full term.
• Payments are equal, made monthly, and occur at the end of each monthly period.
• Interest is modelled monthly at APR divided by 12. The 360-day convention is not applied as a daily count in this calculation.
• Fees, taxes, insurance, PMI, escrow, late charges, and extra payments are not included.

What a 360-Day Accrual Convention Means

A 360-day convention is a way to measure time when calculating interest. Often called “30/360,” it treats each month as 30 days and the year as 360 days for the relevant interest calculation. Other contracts use a 360-day denominator but count the actual number of elapsed days; this is commonly described as actual/360. These methods are not interchangeable, and contract language determines which applies.

With simple daily accrual, a basic calculation is: interest = balance × annual rate × days ÷ day-count denominator. For example, at 8% on a $20,000 balance for 30 days, an actual/360 calculation gives $20,000 × 0.08 × 30 ÷ 360 = $133.33 before any payment or other adjustment. The same 30-day span under actual/365 gives about $131.51. A 30/360 method can produce the same result for a 30-day month, but results can differ for periods of other lengths.

That illustration is not the calculator’s payment formula. A loan can have monthly instalments while interest accrues daily between payment dates. To reproduce that schedule, the calculation generally needs dates, the outstanding balance over time, the applicable day-count method, and the lender’s rounding and payment-allocation rules.

How to Use and Read the Estimate

Enter the original amount borrowed, the annual rate stated for the calculation, and the term in years. The first result is the estimated monthly principal-and-interest payment; the second is estimated interest over the full term if every scheduled payment is made as assumed. The total of payments would be the displayed interest plus principal, or the rounded payment multiplied by the number of months.

• Use the loan principal rather than the amount you hope to borrow after fees unless those fees are included in the amount financed.
• Enter the rate as a percentage: enter 8 for 8%, not 0.08.
• Convert a term expressed in months to years by dividing by 12, or use the matching number of whole years when applicable.
• For a lender’s actual daily-accrual schedule, check the note or payment disclosure for the day-count convention, payment dates, and rounding method.

The payment is not necessarily the full amount due on a bill. Charges such as fees or escrow items can be collected separately or included in a payment, depending on the agreement. The calculator also assumes no skipped, late, or additional payments.

360-Day Accrual Compared with Monthly and Actual-Day Methods

“360-day year” alone does not tell you how a loan’s payment is computed. In a monthly amortization model, the periodic rate is commonly represented as APR divided by 12. In an actual/360 daily method, interest for each period depends on the actual number of elapsed days and uses 360 as the denominator. Actual/365 instead uses 365, while 30/360 uses an agreed convention for counting months and days. The amount of interest can therefore vary with the method and the dates, even when the stated annual rate is the same.

A scheduled payment can also be set independently of the exact day-by-day interest accrual. For example, a lender may establish a regular payment amount but adjust a final amount, or calculate each period’s interest from the balance and elapsed days. Do not assume that a calculator using APR divided by 12 recreates those contract-specific details. Ask for the payment schedule or an explanation of the day-count basis if exact reconciliation matters.

Common Sources of Difference

• Different meaning of “360-day”: actual/360 and 30/360 count days differently.
• Payment dates: a 28-day period and a 35-day period accrue different daily interest when the balance and rate stay the same.
• Rounding: rounding each period’s interest can create a small difference from rounding only the final payment estimate.
• Changing balances or rates: extra principal payments, variable rates, or an irregular first period break the fixed-payment assumptions.
• Other amounts due: fees and other charges are outside this principal-and-interest estimate unless represented in the loan amount or rate.

If a lender’s quoted payment differs, compare the principal, term, rate, number and timing of payments, and day-count basis before attributing the difference to an error. The lender’s disclosure is the source for the contract’s stated figures and assumptions.

Frequently Asked Questions

Does this calculator use a 360-day year for every day of interest?
No. It estimates a monthly payment using APR divided by 12. It does not count actual days or apply a 360-day denominator period by period.

How do I calculate interest using actual/360?
For a simple period, multiply the outstanding balance by the annual rate and the actual number of elapsed days, then divide by 360. The agreement may specify additional details, such as how payments and rounding affect the balance.

Is actual/360 the same as 30/360?
No. Actual/360 uses the actual elapsed day count with a 360-day denominator. 30/360 follows a convention that treats months as 30 days; exact convention details can vary by contract.

Why is the lender’s payment different from the calculator?
Possible reasons include daily accrual, different payment dates, a different day-count convention, fees, irregular first or last periods, or period-by-period rounding. Check the loan disclosure and payment schedule for the method used.

Can I use this estimate for a variable-rate loan?
Only as a fixed-rate illustration for the rate entered. It does not project future rate changes, payment resets, or lender-specific adjustment rules.

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

Related

• Loan Payment Calculator: How Compounding Interest Works
• Loan Calculator Using Payment Amount: Find Loan Size
• Loan Payment Calculator Amortization Schedule Explained

in p | Loan amount | $ | 20000 | 1 | 100000000
in apr | Interest rate (APR) | % | 8 | 0.01 | 100
in yrs | Loan term | years | 5 | 0.0833 | 50
out pmt | Monthly payment | $ | round(p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)), 2) | 2
out int | Total interest | $ | pmt * yrs * 12 - p | 2