What Is Per Diem Interest and How to Calculate It on Your Mortgage

Per diem interest is a daily charge on your mortgage loan from the closing date through the end of that month. Lenders collect this cost at closing before your first regular payment. Understanding this charge helps you prepare for your upfront costs at the closing table. For a complete overview of conventional loan options, see our main guide.

What Is Per Diem Interest?

What is per diem interest? It's the interest your lender charges for each day between your loan closing and the last day of that month. Your lender calculates this by dividing your annual interest rate by 365 days. This daily rate is then multiplied by your loan amount to find your daily interest charge.

This cost shows up in your closing costs as a line item. It represents the interest that builds up before your first official mortgage payment is due. Most conventional loan products include per diem interest as a standard part of the closing process. See seller concessions on conventional loans to reduce your out-of-pocket expenses.

Why Lenders Charge This Cost

Lenders charge per diem interest to get paid for lending you money during the gap between funding your loan and when your regular payment cycle starts. Mortgage interest works in arrears, meaning you pay for the month that just passed. Per diem interest paid at closing covers those initial days, so your payment schedule stays consistent for the rest of the loan.

How to Calculate Per Diem Interest on a Mortgage Loan

How to calculate per diem interest on a mortgage loan is simpler than you might think. You need three pieces of information: your loan amount, your annual interest rate, and your closing date. Follow these steps to find your exact per diem cost. Use our per diem interest calculator to quickly estimate your specific charge.

Step-by-Step Calculation Method

Step 1: Find Your Daily Interest Rate
Divide your annual interest rate by 365. For a 3% interest rate, the math looks like this: 0.03 ÷ 365 = 0.00008219.

Step 2: Calculate Your Daily Interest Charge
Multiply the daily rate by your loan amount. With a $100,000 loan: 0.00008219 × $100,000 = $8.22 per day.

Step 3: Count the Days Until Month End
Figure out how many days pass from your closing date to the last day of that month. If you close on the 15th, count 16 days (the 15th counts as day one).

Step 4: Find Total Per Diem Interest
Multiply the daily charge by the number of days. Using our example: $8.22 × 16 days = $131.52 in per diem interest.

Real-World Calculation Example

Let's say you're closing on a $250,000 mortgage at 4.5% interest on June 20th. Here's how how to calculate per diem interest on a mortgage works:

Daily rate: 0.045 ÷ 365 = 0.00012329
Daily charge: 0.00012329 × $250,000 = $30.82
Days from June 20th to June 30th: 11 days
Total per diem: $30.82 × 11 = $338.99

This $338.99 would be due at your closing table. For large loan amounts, this cost can reach several hundred dollars or more. Check today's mortgage rates to see how your rate affects this calculation.

How Do You Calculate Per Diem Interest on a Mortgage Payoff?

How do you calculate per diem interest on a mortgage payoff? The process is nearly the same, but the timeline changes. When you pay off your mortgage early or refinance, per diem interest covers the days from your last regular payment to your payoff date.

Use the same formula, but count only the days you held the loan balance after your final scheduled payment. Most lenders calculate this amount when you request a payoff quote, so you'll know the exact figure before closing.

How Do I Calculate Per Diem Interest on a Mortgage?

How do i calculate per diem interest on a mortgage? It's the same process we outlined above, but here's a quick reference for common loan amounts and rates:

Loan Amount	Interest Rate	Daily Charge	10 Days	15 Days
$150,000	3.5%	$14.38	$143.84	$215.75
$200,000	4.0%	$21.92	$219.18	$328.77
$250,000	4.5%	$30.82	$308.21	$462.31
$300,000	5.0%	$41.10	$410.96	$616.44

This table shows estimates only. Your actual cost depends on your exact closing date and the number of days counted.

Factors That Change Your Per Diem Interest Cost

Three main factors control how to calculate per diem interest on a mortgage payoff or any mortgage:

• Loan Amount: A larger principal balance means a higher daily interest charge. A $300,000 loan costs more per day than a $150,000 loan.
• Interest Rate: Your annual interest rate directly sets your daily rate. A 5% rate creates a higher daily charge than a 3% rate.
• Closing Date: This is the biggest variable. Closing early in the month means more days of per diem interest. Closing on the 28th versus the 5th saves you thousands of dollars. Review our conventional loan Q&A for more closing strategies.

How You Calculate Per Diem Interest on a Mortgage Payoff Affects Timing

How do you calculate per diem interest on a mortgage payoff determines when your first payment is due. Most lenders schedule your first payment for one full month after the first day of the month following your closing.

If you close on June 15th, your first payment is due August 1st. The per diem interest you paid at closing covers the time from June 15th through June 30th. July 1st passes without a payment because that month is already covered. This system gives you a buffer before regular payments start.

Managing Your Per Diem Interest Cost

You cannot avoid per diem interest on a new purchase. However, you can control how much you pay:

• Schedule Closing Later in the Month: Closing in the last week cuts the number of days significantly. Closing on the 28th instead of the 8th saves you about 20 days of interest.
• Get Precise Numbers Early: Ask your lender for a detailed per diem calculation before closing. This lets you plan your cash needs accurately.
• Review Your Closing Disclosure: Check this document carefully to confirm the per diem interest matches your loan terms and closing date.
• Compare Loan Scenarios: Run the numbers for different closing dates to see the impact on your total costs.

Per Diem Interest and Your Closing Costs

Per diem interest adds to your upfront cash requirement at closing. For a large loan with an early-month closing date, this can add hundreds or even thousands of dollars to your total costs. It does not change the total interest you pay over the life of the loan, but it does increase your immediate expense. Understanding mortgage escrow accounts helps you understand other components of your monthly payment.

Budget for this cost when planning your down payment and closing funds. Talk with your lender about what to expect before you sit down at closing.

Frequently Asked Questions About Per Diem Interest

Is per diem interest the same as prepaid interest?

Yes, per diem interest and prepaid interest refer to the same charge. Per diem interest is a specific type of prepaid interest that covers only the partial month at the start of your loan. Both terms describe money you pay upfront for interest that builds up before your first regular payment.

Can I add per diem interest to my loan amount?

No, per diem interest must be paid in cash at closing. You cannot finance it into your loan for a standard purchase. Some lenders offer options on refinances, but for most transactions, this cost comes out of your pocket at the closing table.

Does a bigger down payment lower my per diem interest?

Yes, indirectly. A larger down payment reduces your total loan amount. Since per diem interest is calculated on the loan amount, a smaller loan means lower daily interest charges and less per diem cost overall. If you put down 25% instead of 10%, your per diem interest drops along with your loan size. Use our affordability calculator to determine your optimal down payment strategy.

Is per diem interest tax-deductible?

Generally, yes. Per diem interest paid at closing counts as mortgage interest and is tax-deductible in the year you close on your home. Consult a tax professional about your specific situation, as rules vary based on your circumstances.

How does per diem interest work on a refinance?

On a refinance, you pay per diem interest from your new loan's closing date through the end of that month. Your old loan also has interest charged up to the day before closing, which the refinance proceeds typically cover. The calculation method stays the same, but you may have per diem costs from both loans if the timing creates overlap. Learn about cash-out refinance options if you're considering tapping equity.

Related Mortgage Concepts You Should Know

Understanding per diem interest is one piece of the bigger mortgage puzzle. These related topics also affect your closing costs and loan terms:

• Discount Points: These upfront fees lower your interest rate. One point typically costs 1% of your loan amount and reduces your rate by about 0.25%.
• Private Mortgage Insurance (PMI): Lenders require PMI on conventional loans with less than 20% down. This insurance protects the lender if you stop paying. See when conventional loans require PMI for details.
• Debt-to-Income Ratio (DTI): Lenders use this number to decide if they approve your loan. Your total monthly debt payments divided by your gross monthly income cannot exceed a certain percentage.
• Closing Costs: Per diem interest is just one part of your total closing costs, which also include appraisal fees, title insurance, and lender fees.

Bottom Line

Per diem interest is a predictable and calculable cost in the home buying process. By learning what it is, how to calculate per diem interest on a mortgage, and how it affects your closing, you enter the process with confidence and accurate financial expectations. For a complete list of planning tools, visit our mortgage calculators hub. Always ask your mortgage lender for precise figures based on your specific loan and closing date.