Per Diem Interest Calculator: Calculate Your Daily Charges

Calculating per diem interest doesn’t have to be complicated. In just three easy steps, you can figure out exactly what you’ll owe from closing to your first payment. Save time, reduce surprises, and take control of your finances with this simple guide.

Loan Amount ($)

Interest Rate (%)

Closing Date

Days in Year

Click the number to change the year

Per Diem Interest: This is the daily interest charged from your closing date until the end of the month. It’s collected at closing and covers the gap between when you receive the loan and when regular payments begin. Formula: (Loan Amount X Interest Rate X Days in Year = Days Charged.

What is Per Diem Interest?

When you take out a mortgage, your first full monthly payment usually isn’t due until the second month after you close. For example, if you close in January, your first mortgage payment will typically be due on March 1. Similarly, if you close in March, your first payment comes due in May.

This happens because mortgage interest is paid in arrears - meaning each payment covers the previous month’s interest. Understanding this timeline is key, and a per diem interest calculator helps you plan by showing how much daily interest you’ll owe from your closing date through the end of the month before regular payments begin.

Think of per diem interest as an interest only payment for the closing month.

How the Per Diem Interest Calculator Works

Our per diem interest calculator takes the guesswork out of closing costs. Enter your loan amount, interest rate, and closing date, and the calculator instantly shows your daily interest charge and the total per diem interest due at closing. This is the same daily interest calculation your lender uses to determine the prepaid interest line item on your Closing Disclosure.

The calculator supports three day-count conventions: 365 days, 360 days, and 366 days for leap years. Most lenders use a 365-day year for USDA loans, but some use 360. Check with your loan officer if you're unsure which one applies to your mortgage.

Why Per Diem Interest Matters for USDA Loans

USDA loans have specific closing cost rules, and per diem interest is one of the standard prepaid items you'll see on your Closing Disclosure. Understanding this charge helps you budget accurately for closing day and avoid last-minute surprises. It also helps you compare loan estimates from different lenders on an apples-to-apples basis.

If you're still exploring USDA loan options, our USDA loan calculators page has tools for monthly payments, affordability, and more. You can also review common USDA loan questions to understand other closing costs you might encounter.

Frequently Asked Questions About Per Diem Interest

What is per diem interest on a mortgage?

Per diem interest is the daily interest charge on your mortgage loan from the day you close until the end of that month. It's collected at closing and covers the gap between when your loan funds and when your first regular monthly payment is due.

How is per diem interest calculated?

Per diem interest is calculated by multiplying your loan amount by your annual interest rate, then dividing by the number of days in the year (365, 360, or 366). The result is your daily interest charge. Multiply that by the number of days from closing to month-end to get your total per diem interest.

Why do I have to pay per diem interest at closing?

Mortgage interest is paid in arrears, meaning your monthly payment covers the previous month's interest. Since your first payment isn't due until the second month after closing, the per diem interest collected at closing covers the interest for the partial month between your closing date and the start of your first full payment period.

Does per diem interest use a 360-day or 365-day year?

It depends on your lender and loan type. Some lenders use a 365-day year for per diem interest calculations, while others use 360 days. USDA loans typically use a 365-day year, but you should confirm with your lender. Using 360 days results in a slightly higher daily interest charge.

Can I avoid paying per diem interest?

No, per diem interest is a standard closing cost on most mortgages. It's not a fee you can negotiate away because it represents actual interest owed for the days you have the loan before your first payment period begins. However, closing later in the month reduces the number of days charged.

Related USDA Loan Resources

If you're preparing for closing on a USDA loan, these resources can help you plan:

USDA Loan Calculators – Monthly payments, affordability, and more
How to Apply for a USDA Loan – Step-by-step application guide
Seller Concessions on USDA Loans – Can the seller pay closing costs?
USDA Loan Questions & Answers – Common questions answered