What is per diem interest on a mortgage?

Per diem interest is the daily interest charged on your mortgage loan from your closing date through the end of that month, until your first regular mortgage payment begins. It covers the gap between when you receive the loan and when scheduled payments start. This charge appears on your Closing Disclosure and is collected at the closing table.

How do you calculate per diem interest?

Per diem interest is calculated using this formula: (Loan Amount × Annual Interest Rate) ÷ Days in Year × Number of Days Charged. For example, a $300,000 loan at 6.5% over 365 days equals $53.42 daily interest. If you close on the 15th of a 31-day month, you pay per diem for 17 days (15th through 31st), totaling $907.14.

How many days of per diem interest will I owe at closing?

You pay per diem interest from your closing date through the last day of that month. Close on the 5th = 27 days of charges. Close on the 15th = 17 days. Close on the 25th = only 7 days. Closing late in the month significantly reduces your per diem interest cost.

Does 360 vs 365 days in year matter for per diem?

Yes, it impacts your daily rate. Using 360 days produces a higher daily interest rate than 365 days. For a $300,000 loan at 6.5%: the 360-day method yields $54.17/day, while the 365-day method yields $53.42/day. Confirm which convention your lender uses, as it affects your total per diem cost.

Is per diem interest part of my closing costs?

Yes. Per diem interest appears on your Closing Disclosure as a separate charge and is included in your total cash needed to close. It's a standard closing cost that all lenders collect because they must charge interest from closing through your first payment.

Can I reduce per diem interest by choosing my closing date?

Yes. Closing late in the month significantly reduces per diem charges because fewer days remain between closing and month-end. Many buyers strategically schedule closings for the last week of the month to minimize this cost. Some sellers also cover per diem interest as part of closing cost concessions.

Per Diem Mortgage Interest Calculator

Calculate your per diem mortgage interest instantly with this free tool. Per diem interest is the daily interest your lender charges from your closing date through the end of that month, until your first regular mortgage payment begins. Understanding this charge helps you budget accurately for closing costs and know exactly what you'll owe at settlement.

Calculate Your Per Diem Interest

Loan Amount ($)

Interest Rate (%)

Closing Date

Days in Year

Select the year convention your lender uses

What This Shows: Per diem interest is the daily interest charge from your closing date through month-end. It's collected at closing and appears on your Closing Disclosure. The amount depends on your loan amount, interest rate, and how many days remain in the month after closing. To minimize this cost, consider closing late in the month. Learn more about other closing cost assistance options.

What Is Per Diem Interest?

Per diem interest is the daily interest charge on your mortgage loan. It represents the amount of interest that accrues each day between your loan closing date and your first official mortgage payment. This charge is standard on all conventional loans and appears as a separate line item on your Closing Disclosure. Understanding per diem interest helps you anticipate total closing costs and verify charges before settlement day.

How Per Diem Interest Works at Closing

When you close on a mortgage, your loan funds transfer to the seller immediately, but your first regular monthly mortgage payment isn't due for a full month or more. During this gap, interest still accrues on your loan balance. Per diem interest fills this gap by calculating what you owe on a daily basis, from closing day through month-end.

Real-World Example: If you close on January 15th and your first payment is due March 1st, your lender charges per diem interest for all days in January (from the 15th through the 31st). This is 17 days of interest charges. The lender adds this to your closing costs, and you pay it at the closing table.

For detailed information on all closing costs and how they're calculated, review our per diem calculation guide.

Per Diem Interest Formula and Example

Calculating per diem interest uses this straightforward formula:

(Loan Amount × Annual Interest Rate) ÷ Days in Year × Number of Days from Closing to Month-End = Total Per Diem Interest

Step-by-Step Calculation Example

Let's assume you're borrowing $300,000 at a 6.5% annual interest rate and closing on January 15th with a 365-day year convention.

Step 1: Calculate Daily Interest Rate
Daily rate = ($300,000 × 0.065) ÷ 365 = $19,500 ÷ 365 = $53.42 per day

Step 2: Count Days from Closing Through Month-End
Days charged = 17 (January 15th through January 31st, including the closing date)

Step 3: Calculate Total Per Diem
Total per diem = $53.42 × 17 = $907.14

This $907.14 appears on your Closing Disclosure and is collected at your closing. Use the per diem calculator above to estimate your specific charge in seconds.

When Per Diem Interest Appears on Your Closing Disclosure

Per diem interest always shows on your Closing Disclosure, the official settlement document provided at least three business days before closing. It appears as a separate charge under "Interest" or "Finance Charges." Most lenders collect this charge at closing and include it in your total cash needed to close. You cannot avoid paying per diem interest—all lenders charge it. However, you can reduce the amount by choosing your closing date strategically.

Some sellers help cover per diem interest as part of seller concessions, though this varies by market and your negotiating position.

How Your Closing Date Affects Per Diem Interest

Your closing date has a dramatic impact on per diem interest. Closing early in a month means more days until your first payment, so more per diem interest. Closing late in the month means fewer days of per diem charges. This is one of the few closing costs you can directly control.

Per Diem Comparison by Closing Date

For a $300,000 loan at 6.5% interest (365-day year), here's what you'd pay with different closing dates:

Close on January 5th: 27 days of per diem = $1,442.34
Close on January 15th: 17 days of per diem = $907.14
Close on January 25th: 7 days of per diem = $373.94
Close on January 31st: 1 day of per diem = $53.42

Closing on the 31st saves you $1,388.92 compared to closing on the 5th. Many savvy buyers strategically schedule their closings for late in the month to reduce this cost. Review our conventional loan Q&A for more closing strategies.

The Difference Between Per Diem Interest and Your Monthly Payment

Per diem interest is separate from your regular monthly mortgage payment. Your monthly payment begins the month after your closing and includes:

Principal (the amount borrowed)
Interest (monthly interest charge)
Property Taxes
Homeowners Insurance
Private Mortgage Insurance (PMI) if your down payment is less than 20%

Per diem interest is a one-time charge collected only at closing. It's not rolled into your monthly payment. Understanding these differences helps you plan your closing budget accurately. Learn more about how mortgage escrow accounts work with your monthly payments.

Per Diem Interest vs. Other Closing Costs

Per diem interest is just one of many closing costs you'll encounter. Other costs typically include loan origination fees, appraisal fees, title insurance, attorney fees, and property taxes. Unlike some of these costs, per diem interest cannot be avoided—but you can minimize it with strategic timing. Use our mortgage calculators to estimate all your closing costs and total monthly payment.

360-Day vs. 365-Day Year: Which Convention Does Your Lender Use?

Some lenders use a 360-day year (banker's year) for interest calculations, while others use 365 days. This choice affects your daily interest rate slightly. With a 360-day year, you're dividing your annual interest by fewer days, resulting in a higher daily rate. Let's compare:

$300,000 loan at 6.5% interest:

365-day year: $53.42 daily interest
360-day year: $54.17 daily interest

Over 17 days of per diem, this difference adds up to about $13. Always confirm which convention your lender uses and verify it on your Closing Disclosure. Most conventional lenders use 365 days, but it's worth asking during the pre-approval process.

Why Understanding Per Diem Interest Matters for Your Home Purchase

Understanding per diem interest helps you:

Budget accurately for total closing costs and cash needed at settlement
Choose an optimal closing date to minimize interest charges
Review your Closing Disclosure with confidence and catch errors
Compare lender estimates and closing cost breakdowns fairly
Negotiate closing cost help from sellers, knowing which costs to prioritize
Avoid surprises and unexpected charges at the closing table

For a complete planning toolkit, visit our mortgage calculators hub where you'll find tools for payments, affordability, refinancing, and more.

Frequently Asked Questions About Per Diem Interest

What happens if I close on the very last day of the month?

You'll pay only one day of per diem interest, which can save you hundreds of dollars compared to closing mid-month. For the $300,000 example above, closing on January 31st costs just $53.42, while closing on January 5th costs $1,442.34.

Can per diem interest change after I receive my Closing Disclosure?

Per diem interest is calculated based on your loan amount, interest rate, and closing date. Once your Closing Disclosure is issued (three days before closing), the per diem amount is locked in and will not change. However, verify the calculation is correct before signing at closing.

Do all mortgage lenders charge per diem interest?

Yes. Every mortgage lender charges per diem interest. It's a standard part of mortgage lending because the lender must charge interest from closing through your first payment. You cannot avoid this charge, but you can minimize it with strategic closing date selection.

Will per diem interest be rolled into my mortgage principal?

No. Per diem interest is paid separately at closing. It is not added to your loan amount or financed into your mortgage. You pay it as a one-time charge on settlement day, similar to other closing costs like appraisal fees or title insurance.

Is per diem interest tax-deductible?

In some cases, yes. Points and certain prepaid interest may be deductible on your tax return, but rules are complex and vary by situation. Consult a tax professional or CPA for guidance on deducting mortgage interest and closing costs for your specific circumstances.

How does per diem interest affect my first mortgage payment date?

Your first regular mortgage payment is typically due on the first day of the second month following your closing. If you close in January, your first payment is usually due March 1st. Per diem interest covers all interest from your January closing through February.

Can I reduce per diem interest by putting down more money?

Your down payment amount doesn't affect per diem interest. Per diem is based on your loan amount, interest rate, and closing date. A larger down payment means a smaller loan amount, which does reduce per diem charges. However, the main lever you control is your closing date—closing late in the month always saves the most.

Bottom Line: Per diem mortgage interest is a normal and expected closing cost that covers daily interest from your closing date through month-end. By understanding how it's calculated and choosing your closing date strategically, you can minimize this cost and budget accurately for settlement day. Use this calculator to estimate your specific per diem charge in seconds.