Daily Interest Calculator: How to Calculate Daily Interest
Learn how to calculate daily interest, daily interest on a loan, and average daily balance style interest with clear formulas and examples.
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Searching daily interest calculator usually means you want to know how much interest builds up each day on a loan, credit card, savings account, or overdue balance. Daily interest calculations are used in consumer loans, mortgages, credit cards, and many types of business financing. Knowing how to calculate it helps you understand borrowing costs and the benefit of making early payments.
The Daily Interest Formula
Daily interest = Balance ร (Annual rate รท 365)
Convert the annual rate to a decimal before dividing:
Example: Annual rate of 8% = 0.08
Daily interest = Balance ร (0.08 รท 365)
Numerical example:
- Balance: $12,000
- Annual rate: 8%
Daily rate = 0.08 รท 365 = 0.00021918
Daily interest = 12,000 ร 0.00021918 = $2.63 per day
Monthly interest = $2.63 ร 30 โ $78.90 per month
Using 360 vs 365 Days
Some lenders use a 360-day convention instead of 365. This is common in commercial lending and certain mortgage products (bank method).
360-day method:
Daily interest = Balance ร (Annual rate รท 360)
Example: $12,000 at 8%:
Daily interest = 12,000 ร (0.08 รท 360) = 12,000 ร 0.000222 = $2.67 per day
The 360-day method produces slightly higher daily interest than 365. Always check your loan agreement to see which convention applies.
Daily Interest on a Personal Loan
Most personal loans use simple daily interest (also called simple interest). The formula above applies directly.
As you make payments that reduce the principal balance, the daily interest charge decreases because it is recalculated on the lower remaining balance.
Example: $10,000 personal loan at 12% APR
At start of loan:
Daily interest = 10,000 ร (0.12 รท 365) = $3.29 per day
After 12 monthly payments (assuming principal paid down to $8,500):
Daily interest = 8,500 ร (0.12 รท 365) = $2.79 per day
This is why making extra principal payments early in a loan saves more interest than paying the same amount later.
Daily Interest on a Mortgage
Mortgages typically accrue interest daily. Most mortgages use simple daily interest, not compound.
The standard mortgage payment calculation uses the monthly rate (annual rate รท 12), but the daily accrual rate (รท 365 or รท 360) affects prepayment calculations and per-diem interest.
Per diem interest (for closing costs):
When you close on a home purchase, the lender charges interest for each day from the closing date through the end of that calendar month. This is called the โprepaid interestโ at closing.
Formula:
Daily interest = Loan amount ร (Rate รท 365)
Per diem at closing = Daily interest ร Days remaining in month
Example:
$350,000 mortgage at 6.5% APR, closing on the 15th of a 30-day month.
Daily interest = 350,000 ร (0.065 รท 365) = $62.33 per day
Days remaining: 30 โ 15 = 15 days
Prepaid interest = 62.33 ร 15 = $934.97
This amount is collected at closing, after which your first full monthly payment begins on the 1st of the following month.
Daily Interest on Credit Cards
Credit cards often calculate interest using the Average Daily Balance (ADB) method. Instead of charging interest on a single balance, the issuer calculates the average balance across all days in the billing cycle, then applies the daily periodic rate.
Step 1: Calculate the daily periodic rate
Daily rate = APR รท 365
Example: 22% APR
Daily rate = 0.22 รท 365 = 0.0006027 (0.06027% per day)
Step 2: Calculate the average daily balance
Add up your balance for each day of the billing cycle (typically 28โ31 days) and divide by the number of days.
Example (simplified 10-day cycle):
| Day | Balance |
|---|---|
| 1โ5 | $2,000 |
| 6โ8 | $2,800 (after $800 purchase on day 6) |
| 9โ10 | $1,300 (after $1,500 payment on day 9) |
Sum of daily balances: (2,000 ร 5) + (2,800 ร 3) + (1,300 ร 2)
= 10,000 + 8,400 + 2,600 = 21,000
Average daily balance = 21,000 รท 10 = $2,100
Step 3: Calculate interest for the cycle
Interest = Average daily balance ร Daily rate ร Days in cycle
Interest = 2,100 ร 0.0006027 ร 10 = $12.66
How Making Payments Affects Daily Interest
Since daily interest accrues on the current balance, making payments reduces the balance and thus reduces future interest.
Why paying early helps:
If you have a $5,000 loan at 10% APR and make an extra $500 payment on the 10th day of the month (instead of the 30th):
You save 20 extra days of daily interest:
Daily interest on $500 = 500 ร (0.10 รท 365) = $0.137 per day
20 days ร $0.137 = $2.74 in saved interest for this one payment
Small by itself, but repeated monthly over a 5-year loan, early payments meaningfully reduce total interest paid.
Why Daily Interest vs Monthly Interest
Many loan quotes use the monthly interest rate for simplicity:
Monthly rate = Annual rate รท 12
Example: 12% APR = 1% per month
Monthly interest on $10,000 = $100
This is a useful approximation but not exactly equal to 30 days of daily accrual.
Exact 30-day daily accrual at 12% APR:
Daily rate = 0.12 รท 365 = 0.0003288
30-day interest = 10,000 ร 0.0003288 ร 30 = $98.63
The small difference ($100 vs $98.63) matters in precise amortization calculations.
Interest-Free Periods on Credit Cards
Most credit cards have a grace period โ typically 21โ25 days after the statement close date. If you pay the full statement balance before the due date, no interest is charged on purchases.
Interest only begins accruing daily when:
- You carry a balance past the due date
- You take a cash advance (usually no grace period)
- You miss a payment entirely
This is why paying the full balance monthly eliminates credit card interest charges entirely, even on a high-APR card.
Common Daily Interest Mistakes
Forgetting to convert percent to decimal โ entering 8 instead of 0.08 produces a result 100 times too large.
Using the wrong number of days โ some contracts use 360, others 365. The difference adds up over years.
Applying the daily rate to the wrong balance โ use the outstanding principal, not the original loan amount, after payments have been made.
Not checking for compounding โ most personal loans use simple daily interest, but some products compound daily. Compounding produces more interest over time.
The Bottom Line
To calculate daily interest, divide the annual interest rate by 365 (or 360 per your contract) and multiply by the current balance. For loans, the daily charge decreases as you pay down the principal. For credit cards, the average daily balance method applies the daily rate to an average of your balance throughout the billing cycle.
Use the Loan Calculator for full loan payment and interest estimates across different terms and rates.
How to Calculate: Step-by-Step Guide
Find the annual rate
Use the APR or yearly interest rate as a percentage.
Convert it to a daily rate
Divide the annual rate by 365 unless your contract uses a different day-count rule.
Multiply by the balance
Apply the daily rate to the current principal or average daily balance.