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.

Current balance

Annual rate

Days

Day-count convention

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.

Editorial noteMaintained by EveryCalc - Reviewed June 2026

EveryCalc calculators are designed for fast, practical estimates with transparent inputs and no required account. We use plain formulas, visible assumptions, and related tools so visitors can check the result from more than one angle.

Results are informational only. For financial, tax, legal, medical, construction, or other high-impact decisions, verify the output against primary sources or a qualified professional.

Learn more about our review process on the EveryCalc methodology page.

How this calculator works

What this page estimates

This Daily Interest Calculator is built to give a quick, browser-based estimate for daily interest. 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. The inputs stay on the page during normal use, and the result should be treated as an estimate for planning, comparison, or education rather than professional advice.

Calculation approach

The calculator applies the standard relationship implied by the inputs, then formats the answer so it can be checked and reused. For finance tools, the most important step is using consistent units, rates, time periods, and assumptions before comparing the result with another calculator or outside quote.

Example workflow

For example, start with a realistic value you already know, change one input at a time, and watch how the answer moves. That makes it easier to tell whether the result is being driven by the main amount, the rate, the time period, or a unit conversion.

Practical checks

Use current, real-world numbers when the result affects money, health, tax, or legal decisions.
Run a low, base, and high case when the inputs are estimates.
Check the related calculators below when the next decision depends on a different assumption.

How to interpret the daily interest result

Best use

Use the result as a planning number for comparing payments, rates, returns, tax reserves, or cash-flow choices before you request a quote or make a commitment.

Cross-check

Compare the answer with the contract, lender estimate, tax form, brokerage statement, payroll record, or invoice that will control the real-world outcome.

Watch for

Do not rely on a single optimistic rate, return, or fee assumption. Money pages work best when you run low, base, and high cases and keep professional advice separate from the estimate.

This page belongs to the Finance calculator library, so the answer should be read in the context of the decision you are modeling rather than as a universal rule.

Before relying on this daily interest estimate

Most calculator mistakes come from the inputs, not the arithmetic. Use this short audit before you reuse the answer in a spreadsheet, quote, application, or important conversation.

Confirm source numbers

Match balances, rates, fees, taxes, income, and payment dates against the lender quote, payroll record, tax form, statement, invoice, or contract.

Separate cash flow from total cost

A lower monthly payment can still cost more over time if fees, interest, taxes, or a longer term are hidden in the structure.

Run conservative cases

Test at least one higher-cost or lower-return case before using the output for a purchase, refinance, investment, loan, or tax decision.

Rerun this page when the rate, price, term, fee, tax rule, income, expense, or expected holding period changes.

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.