Daily Interest Calculator
This calculator shows the exact dollar amount of interest a balance earns or a loan costs in a single day. Enter a Principal Balance and an Annual Interest Rate (APR), and the Daily Interest figure — plus its Monthly and Yearly equivalents — updates instantly as you type, right here in the browser.
How to Calculate Daily Interest
Two numbers drive the result: Principal Balance (the current amount on the loan or deposit) and Annual Interest Rate (APR) (the rate as a percentage). The calculator converts the APR to a daily rate using the Days in Year divisor, then multiplies that daily rate by the Principal Balance — the Daily Interest hero number updates on every keystroke, with no button to press and no page to reload.
The Daily Interest Formula
The math behind the hero number is Principal × (Annual Rate ÷ 100) ÷ Days in Year. Below it, Monthly equivalent multiplies that daily figure by 30 days for a rough monthly cost or earning, and Yearly equivalent multiplies it back out by the Days in Year divisor — so the yearly figure always reconciles exactly with the Principal and APR you entered, whichever divisor you're using. This is simple daily interest, not compounding — the same method sometimes called the simple interest per day approach, where each day's charge is figured on the principal alone rather than on interest already added.
Daily Interest on Loans, Credit Cards & Savings
The same formula applies whether the balance is working for you or against you. Loans — mortgages, car loans, lines of credit — charge daily interest on the outstanding principal, so the figure shrinks as you pay the balance down. Credit cards apply a daily rate to whatever you're carrying, which is why balances left unpaid add up faster than a simple loan. Savings accounts use the identical math in reverse — the Daily Interest figure is what the bank credits you, not what it charges. Enter whichever balance and rate applies to see today's exact number.
360 vs. 365 Day Interest — Which Divisor Should You Use?
Tap Advanced options to change the Days in Year divisor. Most credit cards and savings accounts use 365. Some commercial loans and older mortgage conventions use 360 — spreading the same annual rate over fewer days, so each day's interest is very slightly higher. A few banks use 365.25, the exact length of a solar year averaged over leap years. Check your loan or account disclosure for which convention it actually uses, then match the setting here so the number reflects your real statement.
Frequently Asked Questions
How do you calculate daily interest?
Divide the annual interest rate by the number of days in the year to get a daily rate, then multiply that daily rate by the balance. For a $10,000 balance at 5% APR over a 365-day year, that's (5 / 100 / 365) × $10,000 — about $1.37 a day. This calculator runs that exact formula on every keystroke, so there's nothing to work out by hand.
What is the daily interest formula?
The formula is Principal × (Annual Rate ÷ 100) ÷ Days in Year. Principal is the current balance, Annual Rate is the APR as a percentage, and Days in Year is the divisor your lender or account uses — usually 360 or 365. Change any of the three numbers here and the Daily Interest figure updates instantly.
How is daily interest calculated on a loan?
Most loans that charge daily interest — mortgages, car loans, and lines of credit among them — apply the same Principal × (Rate ÷ 100) ÷ Days-in-Year formula to whatever the outstanding balance is that day. As you pay down the principal, the daily interest amount shrinks along with it. Enter your current loan balance and rate here to see today's exact daily charge.
How is daily interest calculated on a credit card?
Credit card issuers almost always use a 365-day divisor and apply the daily rate to your balance every day of the billing cycle, which is why carrying a balance compounds faster than a simple loan. This calculator uses the same math — enter your card's APR and current balance to see the daily and monthly cost of carrying that balance.
What's the difference between 360-day and 365-day interest?
A 360-day divisor spreads the same annual rate over fewer days, so each day's interest is very slightly higher than under a 365-day divisor — a convention some commercial loans and mortgages still use from an era of hand calculation. A 365.25-day divisor, used by a few banks, accounts for the extra quarter-day in the actual solar year. Switch the Days in Year setting here to see the small but real difference for your own numbers.
How do I convert a monthly interest rate to a daily rate?
First convert your monthly rate to an annual rate by multiplying by 12, then enter that annual rate here as the APR — the calculator handles the annual-to-daily step for you. For example, a 0.5% monthly rate is a 6% APR, which this calculator turns into a daily rate of roughly 0.0164% (6 ÷ 100 ÷ 365).
