Choose daily interest amount, daily rate, annual rate, or principal balance. Enter the requested values and match the day-count basis to your loan contract.
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Auto Loan Per Diem Formula
The following formulas estimate daily simple interest using the default 365-day basis. Select 360 or 366 only when your loan terms call for that divisor.
- Where PDI is the per diem interest rate (%)
- PDP is the interest accrued for one day ($)
- I is the annual contract interest rate (%), not an APR that includes fees
- B is the current outstanding principal balance ($)
For a 365-day basis, divide the annual rate by 365 to find the daily percentage. Other day-count conventions depend on the loan contract; this calculator does not infer them from the date.
Auto Loan Per Diem Definition
What is a per diem auto loan?
Per diem means per day. For a daily simple-interest auto loan, interest accrues on the outstanding principal each day.
Daily accrual does not mean payments must be made daily. This estimate does not model precomputed interest or provide a lender payoff quote; balance changes, payment timing, fees and contract rounding affect the amount due.
Example Problem
How to calculate a per diem auto loan?
First, determine the annual contract interest rate. This example uses 8% and a 365-day basis.
Next, calculate the daily percentage by dividing the annual percentage by 365:
8% / 365 ≈ 0.021918%
Next, determine the current principal balance. This example uses $12,000.00 of outstanding principal.
Finally, calculate the interest accrued for one day without rounding the daily rate first.
PDP = (I / 365) / 100 * B
PDP = (8 / 365) / 100 * 12,000
PDP ≈ $2.6301 per day (about $2.63)
