Per Diem Interest Calculator
Daily interest accrual for payoff quotes and closings.
Your Per Diem Interest Calculator Result
Generated from the inputs below — a record you can revisit, or share with anyone helping you plan.
Your detailsInput Parameters
Loan
Example rate, not current market data. Enter the rate on your loan or quote.
Payoff Timing
$18,000 × 6.5% ÷ 365 days. Under a 360-day basis it would be $3 per day.
Balance plus accrued interest. Your lender may add recording or lien-release fees on top.
Every extra day between requesting a payoff quote and the lender receiving funds adds this much.
Analysis
Email me this result
Free financial calculators. Where an official rule applies, the calculator shows the source it was checked against. No sign-up, and every calculation runs entirely in your browser — nothing you type is ever sent to us.
You might also need
Picked based on what this calculator does
365/360 Loan Calculator
The commercial day-count convention and what it really costs.
Open calculatorLoan Payoff Calculator
Pay off any loan early with extra payments.
Open calculatorComplete Loan Calculator
Payment, payoff, and amortization in one.
Open calculatorCar Loan Payoff Calculator
Pay off your auto loan early with extra payments.
Open calculatorInterest Rate Analyzer
APR vs Nominal rate.
Open calculatorCredit Card Interest Calculator
See how daily compounding builds your balance and plan payoff.
Open calculatorPer Diem Interest: The Number Behind Every Payoff Quote
Per diem interest is simply the amount your loan accrues in a single day. It is the figure lenders use to build payoff quotes, prorate interest at closing, and calculate what you owe when a payment lands mid-cycle.
Two details change the answer more than people expect.
The day-count basis. Most consumer loans divide by 365; many commercial loans divide by 360, which makes each day slightly more expensive — $3.2500 instead of $3.2055 in the example above. Your loan agreement specifies which applies. The 365/360 Calculator covers that convention in depth.
Per diem is calculated on the current balance, so it falls as you pay the loan down. A quote generated today will not match one generated next month, which is exactly why payoff quotes carry expiry dates.
The Three Moments Per Diem Actually Costs You Money
1. Paying off a loan. A payoff quote is your balance plus per diem interest for every day until the lender receives funds — not until you send them. Mail a cheque and you may be paying 5-7 extra days of accrual. On a $30,000 balance at 7% that is roughly $5.75 a day, so the difference between wiring and mailing can be $40 or more. Ask for a quote "good through" a specific date and pay by the fastest method available.
2. Closing on a mortgage. Lenders collect prepaid interest from your closing date through the end of that month. Close on the 3rd and you pay ~28 days of per diem at closing; close on the 28th and you pay ~3 days. On a $400,000 loan at 6.5%, that is the difference between roughly $1,993 and $214 in cash at the table. Closing late in the month is a genuine, legal way to reduce cash-to-close — though you then start repayment sooner, so it is a timing shift rather than a saving.
3. Selling a car with a loan on it. The dealer or buyer pays off your lender directly, and the payoff figure includes per diem to the funding date. Knowing your daily rate lets you check their number rather than accepting it.
One caution: your final payoff amount may also include a lien release fee, title transfer cost, or in rare cases a prepayment penalty. Per diem tells you the interest component, not the whole invoice.