Finance category
Mortgage, loan, investing, tax, and money calculators.
Daily Interest Calculator
Compute the daily interest accrual on a mortgage, credit card, or commercial loan balance. Supports Actual/365, Actual/360, and 30/360 day-count conventions used across consumer and commercial finance.
Daily interest
$14.76
Total interest
$442.76
Balance after period
$84,943
Daily periodic rate
0.01747
How the math works
Daily interest accrues on the current balance. Mortgages use Actual/365 (or Actual/366 in a leap year). Many commercial loans use Actual/360 — which produces slightly higher effective rates because the same rate spreads over fewer days. 30/360 is the banker's convention used for bonds and some legacy mortgages.
Mortgage per-diem interest at closing is typically calculated Actual/365. Verify the convention on your specific note — it affects closing costs, escrow refunds, and monthly billing at the margins.
How to Use
- Enter current balance and annual rate.
- Enter number of days in the period.
- Select day-count convention — Actual/365 for most mortgages, Actual/360 for many commercial loans.
Frequently Asked Questions
Why does Actual/360 cost more?
Same annual rate divided by 360 days produces a higher daily rate than dividing by 365. Applied to actual days, the total interest over a year is ~1.4% higher. Watch for this on commercial mortgages.
When does 30/360 apply?
Bond markets and some legacy mortgages use 30/360 — assumes each month has 30 days. Simpler calculation, but creates small discrepancies on month-end cash flows.
How is credit card interest calculated?
Average Daily Balance × daily periodic rate × days in cycle. DPR = APR ÷ 365. Paying early in the cycle reduces ADB and interest charged. Paying in full by the due date avoids interest entirely via the grace period.
Related Calculators
Per Diem Interest Calculator
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Simple Interest Loan Calculator
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Credit Card Interest Calculator
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APR Calculator
Convert to APR.
Prepaid Interest Calculator
Prepaid interest at closing.
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