The loan balance, invoice amount, or other amount interest is based on.
Use the period you want to estimate, such as 7, 30, or 45 days.
Some lenders use a 360-day year, which creates a slightly higher daily cost.
Enter a balance, rate, and number of days to see daily interest
What is a daily interest calculator?
A daily interest calculator shows how much interest builds up each day on a balance, loan, unpaid invoice, or other amount that earns or charges simple interest. Instead of looking only at the annual rate, you can turn that rate into a daily cost and see what each extra day really means in dollars.
This is useful when you are checking a loan payoff quote, estimating late-payment interest, comparing short-term financing options, or calculating the carrying cost of a balance over a specific period. For many real-world decisions, the question is not just “what is the annual rate?” It is “how much does one more day cost me?”
For example, if you owe $10,000 at 8% annual interest, the daily simple interest is about $2.19 using a 365-day year, or about $2.22 using a 360-day year. Over 30 days, that difference adds up. That is why this calculator shows both the daily amount and the total cost for the number of days you enter.
How to use this calculator
Enter the principal or balance. This is the amount interest is based on. It could be a loan balance, overdue invoice, line of credit balance, or any other amount that accrues simple interest.
Enter the annual interest rate. Use the stated yearly rate from your loan agreement, invoice terms, or financing offer. The calculator converts that annual rate into a daily rate automatically, so you do not need to do the math by hand.
Choose the number of days. Enter the period you want to price out, such as 7 days, 30 days, or 45 days. The result shows both the interest per day and the total interest for that period.
Select the day-count method. Many agreements use a 365-day year, but some lenders use a 360-day year, also called Banker’s Rule. If you are unsure, check your contract or compare both methods to see the range.
Use the result to make a decision. If you are comparing borrowing costs, the daily number tells you what waiting costs. If you are reviewing loan repayment options, pair this with our Loan Calculator to see the bigger monthly picture.
This calculator is designed for simple daily interest, not compound interest. If interest is added back to the balance every day and then earns more interest, you will need a compounding calculator instead.