Money Tools

Per Diem Interest Calculator

Estimate daily loan interest and total short-period interest from balance, rate, and day count.

Updated April 18, 2026
Free online tool
Planning and research use

Why this page exists

Closing and payoff figures often depend on a few days of daily interest rather than a full monthly payment amount. This calculator helps visitors estimate daily per diem interest and total short-period interest from a loan balance, annual rate, and number of days.

Interactive tool

Run the estimate

Enter your numbers and read the result first, then use the sections below to understand what affects the outcome.

Calculator

Per diem interest calculator

Estimate daily interest and total short-period interest from a loan balance, annual rate, and day count.

Result

$721

Estimated per diem interest from loan balance multiplied by the annual interest rate and divided by 365, then multiplied by the number of days entered.

Daily interest amount$60.10

Total per-diem interest$721

Loan balance used$325,000

Rate and days used6.75% for 12 days

$325,000 at 6.75% works out to about $60.10 of daily interest using a 365-day convention.
12 days of accrual points to about $721 in this simple estimate.
Use the result as a planning number only, because lenders may use different day-count conventions or contract-specific accrual rules.

This is a simple 365-day daily-interest estimate only. Some lenders use 360-day conventions, exact-day methods, or contract-specific accrual rules that can change the official figure.

Planning note

Last updated April 18, 2026. Use this tool to compare scenarios and plan ahead, then confirm important details with the lender, employer, insurer, contractor, or other qualified provider involved in the final decision.

How it works

What the calculator is doing

Enter the loan balance, annual interest rate, and the number of days you want to price.

The calculator estimates daily interest from balance multiplied by rate and divided by 365.

It multiplies the daily amount by the number of days entered to show the total short-period interest estimate.

Understanding your result

This is a daily-interest planning estimate. It can help with payoff timing or closing math, but official lender figures may differ if the lender uses a different day-count convention or accrual method.

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Examples

Ways people use this tool

Example scenarios help turn a quick estimate into a more useful comparison or planning step.

Estimate interest between closing and first payment

A short daily-interest estimate can help explain why closing timing changes prepaid interest due at settlement.

Check a payoff figure over a short delay

Running the calculation for a few extra days can show how much interest may accrue if payoff timing slips.

When to use it

Good times to run this calculator

Use this when you want to estimate short-period loan interest instead of relying on a full monthly payment figure.

It is especially useful around mortgage closings, payoffs, and any situation where the number of accrued days matters.

Assumptions and limitations

The estimate assumes a 365-day daily-interest convention and a stable annual rate over the days entered.

It does not model lender-specific accrual conventions, fees, escrow items, or unusual payoff timing rules.

Common mistakes

Avoid the usual input mistakes

Using a monthly payment amount instead of the actual loan balance can make the daily-interest estimate meaningless.

Treating the result like an official lender payoff line item can be misleading when the lender uses a different day-count method.

Practical tips

Run the calculator for several nearby closing or payoff dates if timing flexibility is part of the decision.

Use the result with cash-to-close and closing-cost tools if the larger question is how much cash is needed on a specific date.

Worked example

Walk through a realistic scenario

A worked example shows how the estimate behaves when the inputs resemble a real planning decision.

Estimate interest for a short closing window

A buyer wants to see how much daily mortgage interest may accrue between closing and the first payment date.

1. Enter the loan balance, annual interest rate, and the number of days to price.

2. Review the daily interest estimate first so the time sensitivity is clear.

3. Use the total short-period interest to understand how closing timing changes the cash required.

Takeaway: Per diem interest is most useful when a small date change can affect the amount due enough to matter in the closing budget.

FAQ

Common questions

How is per diem interest estimated here?

The calculator multiplies the loan balance by the annual interest rate, divides by 365 to estimate daily interest, and multiplies that daily amount by the number of days entered.

Why might the lender figure be different?

Some lenders use 360-day conventions, exact-day methods, or contract-specific accrual rules, so the official figure may not match a straight 365-day estimate.

When is daily interest most useful?

It is especially useful for short payoff periods and closing windows where even a few days can change the amount due.

Related tools

Keep comparing

Loan-interest, mortgage, cash-to-close, and closing-cost tools help connect the daily-interest estimate to the larger borrowing and closing workflow.

Mortgage-prepayment and budget tools add context when the short interest estimate feeds a broader timing or cash-planning decision.

Money ToolsUpdated April 11, 2026