# Interest Per Day Calculator

URL: https://speedycalculator.com/calculators/finance/interest-per-day/
Last updated: 2026-10-25

> The interest per day calculator works out how much interest accrues each day on a loan, savings or credit balance – the daily interest in money and as a daily rate – and the interest over any number of days.

## Inputs

- Balance
- Annual interest rate (%)
- Day-count basis
- Number of days

## Results

- Interest per day
- Daily interest rate
- Interest for the period
- Interest per month (approx.)

## Formula

```
Daily rate = annual rate ÷ day-count basis (365 or 360)
Interest per day = balance × daily rate
Interest for d days = balance × daily rate × d
```

## Explanation

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

FieldWhat to enterBalanceAmount in your currencyAnnual interest rateIn %Day-count basisChoose one: 365 days, 360 daysNumber of daysA 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:

BalanceInterest per day10,0001.6415,0002.4720,0003.2925,0004.1130,0004.9340,0006.58

## Worked 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.

## FAQ

**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).