Daily interest (also called per diem interest) is used for mortgage payoffs, car loans and student loans. Lenders quote a per diem amount to add to a payoff figure for each extra day.
How to use the Interest Per Day Calculator
- Balance
- Annual interest rate
- Day-count basis
- Number of days
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter the balance, annual interest rate, day-count basis and the number of days.
Tips
- Compare loans by APR and total cost, not just the monthly payment.
- Extra payments go straight to principal and can save a lot of interest.
- Pay off the highest-rate debt first if you want to save the most money.
- Check for prepayment penalties before paying a loan off early.
Common mistakes to avoid
- Stretching a loan term to lower the payment without seeing the extra interest.
- Paying only the minimum on credit cards.
- Forgetting fees that are rolled into the loan.
Inputs explained
| Field | What to enter |
|---|---|
| Balance | Amount in your currency |
| Annual interest rate | In % |
| Day-count basis | Choose one: 365 days, 360 days |
| Number of days | A number |
What each result means
- Interest per day = [Balance]×[Annual interest rate]÷100÷[Day-count basis]
- Daily interest rate = [Annual interest rate]÷[Day-count basis]
- Interest for the period = [Interest per day]×[Number of days]
- Interest per month (approx.) = [Interest per day]×[Day-count basis]÷12
Example values
How the main result changes when Balance changes and everything else stays at the example values above:
| Balance | Interest per day |
|---|---|
| 10,000 | 1.64 |
| 15,000 | 2.47 |
| 20,000 | 3.29 |
| 25,000 | 4.11 |
| 30,000 | 4.93 |
| 40,000 | 6.58 |
Formula
Daily rate = annual rate ÷ day-count basis (365 or 360)Interest per day = balance × daily rateInterest for d days = balance × daily rate × dWorked example
Inputs — Balance: $20,000; Annual interest rate: 6 %; Day-count basis: 365 days; Number of days: 30.
Results — Interest per day = $3.29; Daily interest rate = 0.01644 %; Interest for the period = $98.63; Interest per month (approx.) = $100.00.
Frequently asked questions
How do I calculate daily interest?
Balance × annual rate ÷ 365.
What is per diem interest?
The interest charged per day, often quoted in loan payoff statements.
Why do some lenders use 360 days?
It's a banking convention that slightly increases the daily rate.
What formula does the Interest Per Day Calculator use?
Daily rate = annual rate ÷ day-count basis (365 or 360).