Interest Per Day Calculator
Print| Monthly Interest Accumulation | $0.00 / mo |
The Interest Per Day Calculator enables borrowers, investors, and homeowners to determine the exact amount of interest accruing on a debt or deposit balance every 24 hours. Whether calculating per diem mortgage closing interest, daily student loan interest, credit card finance charges, or daily high-yield savings yield, compute daily interest metrics quickly.
The Daily Interest Formula
Daily simple interest accrual is calculated by converting annual percentage rate (APR) into a Daily Periodic Rate (DPR) and applying it to current principal balance:
Daily Interest Rate (DPR) = Annual Interest Rate (APR) / 365
Daily Interest Amount ($) = Principal Balance × DPR
For accounts featuring daily compounding interest (such as high-yield savings accounts or money market accounts), accrued balance growth uses the daily compounding equation:
Compounded Ending Balance = Principal × ( 1 + (APR / 365) )^Days
Daily Interest Charges by Principal & Rate
Compare daily interest dollar charges (per diem) across common loan balances and APR benchmarks:
| Principal Balance | Annual APR | Daily Rate (DPR) | Interest Cost Per Day | 30-Day Interest Total |
|---|---|---|---|---|
| $10,000 (Student Loan / Car) | 6.50% | 0.0178% | $1.78 | $53.42 |
| $25,000 (Auto / Personal Loan) | 8.99% | 0.0246% | $6.16 | $184.73 |
| $100,000 (Mortgage Balance) | 6.75% | 0.0185% | $18.49 | $554.79 |
| $350,000 (Mortgage Balance) | 6.75% | 0.0185% | $64.73 | $1,941.78 |
Step-by-Step Interest Per Day Calculation Example
Here is an example calculating per diem interest charges for a mortgage closing payout on a $250,000 loan balance:
- Identify Loan Inputs: Principal Balance = $250,000, Interest Rate = 6.25% (0.0625).
- Calculate Daily Interest Rate (DPR):
0.0625 / 365 = 0.00017123 per day (0.017123%). - Multiply by Principal Balance:
$250,000 × 0.00017123 = $42.81 per day. - Calculate 12 Days Per Diem Interest: If closing 12 days before month end:
$42.81 × 12 = $513.72.
Frequently Asked Questions
What is per diem interest in real estate mortgage closings?
Per diem interest is the daily interest charge paid at mortgage closing to cover accrued interest from the closing date through the end of that calendar month.
Do lenders use 365 days or 360 days to calculate daily interest?
Most standard consumer loans and mortgages use a 365-day calendar year. However, commercial loans and traditional banking formulas sometimes use a 360-day year (Banker’s Rule), slightly increasing daily interest charges.
How does paying principal extra reduce daily interest charges?
Because daily interest is calculated directly on your remaining principal balance, making extra principal payments lowers the base balance immediately, reducing daily interest accrual every subsequent day.
What is the difference between simple daily interest and daily compound interest?
Simple daily interest calculates interest strictly on the initial principal. Daily compound interest adds earned daily interest back onto principal, charging interest on previous interest accumulated.