Daily interest calculator
See how much interest accrues every day on your current loan balance — for any loan type.
Calculator loansLogic updated May 2026
This calculator shows how much interest accrues each day on your current outstanding loan balance. Enter your balance, annual interest rate, and any monthly account-keeping fees to see your interest cost broken down by day, week, month, and year. Results are a snapshot at the current balance — they do not project changes as you repay the principal.
How this is calculated
Formula
Daily interest = Balance × (Rate ÷ 100) ÷ 365Step-by-step
- Convert the annual interest rate from a percentage to a decimal (e.g. 12% → 0.12)
- Divide by 365 to get the daily rate
- Multiply by the outstanding balance to get the daily interest amount
- Multiply daily interest by 7 for weekly interest
- For monthly interest, divide the annual rate by 12 and multiply by the balance (the standard monthly convention used by most lenders)
- Annual interest is the balance multiplied by the annual rate as a decimal
- If monthly fees are entered, monthly total cost = monthly interest + monthly fees; annual total cost = annual interest + (monthly fees × 12)
- Rounding mode
- ROUND_HALF_UP
- Precision
- 20-digit internal precision (Decimal.js), rounded to 2 decimal places for display
- Logic last reviewed
Assumptions & limitations
What this calculator assumes
- Simple interest calculation on a static outstanding balance — not an amortising projection
- Daily interest uses a 365-day year (not 360)
- Monthly interest uses balance × rate ÷ 12, consistent with standard lender practice
- Monthly fees are assumed to be a fixed flat amount each month
- The balance is assumed constant — results decrease in practice as you make repayments
- No compounding of interest within the period
- No consideration of leap years
- Tax deductibility of interest (e.g. for investment loans) is not included
What this calculator doesn’t account for
- Does not project how interest decreases as you repay the loan over time
- Does not include one-off fees such as establishment fees or discharge fees
- Does not calculate a comparison rate — add your fees to compare lenders fairly
- Does not model variable-rate changes during the loan term
- Credit card interest may compound daily rather than monthly — this calculator uses simple interest
Worked example
A borrower has $10,000 outstanding on a personal loan at 12% per annum with no monthly fees.
| Input | Value |
|---|---|
| Outstanding balance | $10,000 |
| Annual interest rate | 12% |
| Monthly fees | $0 |
Daily interest: $3.29 — Monthly interest: $100.00 — Annual interest: $1,200.00
At 12% per annum, the daily rate is 12% ÷ 365 = 0.032877%. Applied to $10,000 this gives $3.29 per day. Over a typical month (12 periods per year), that is $100.00. Over a full year it is $1,200.00. As you make repayments and the balance falls, each of these figures will decrease proportionally.
Frequently asked questions
How is daily interest calculated on a loan?
Daily interest = outstanding balance × annual rate ÷ 365. For example, a $10,000 balance at 12% per annum accrues $3.29 per day (0.0328% daily). Most lenders apply this logic to your balance each calendar day, then charge it to your account monthly.
Why does my balance matter more than my interest rate for daily interest?
Daily interest is directly proportional to your balance. Halving the balance halves the daily interest, regardless of the rate. A high balance at a moderate rate can cost more per day than a low balance at a high rate — which is why paying down principal faster has a compounding benefit over time.
How is daily interest different from monthly interest?
This calculator uses balance × rate ÷ 365 for daily interest, and balance × rate ÷ 12 for monthly interest. The monthly figure matches the standard lender convention for scheduled repayments. Some lenders calculate monthly interest as daily interest × days in month, which can produce a slightly different figure depending on the month.
Does this work for credit cards?
Yes — enter your current credit card balance, the purchase interest rate, and any monthly card fees. Note that credit card interest typically compounds daily (interest charges are added to the balance and accrue their own interest), while this calculator uses simple interest. The daily figure will be accurate; the monthly and annual figures may understate total cost slightly for high balances carried for multiple months.
How can I reduce the daily interest I'm paying?
The most direct way is to reduce the outstanding balance — even a small lump-sum repayment immediately reduces your daily interest. If you have a mortgage, an offset account achieves the same effect by reducing the balance for interest calculation purposes without requiring you to redraw later. You can also compare lenders: use the loan comparison calculator to see the interest-rate difference in dollar terms.
Why is my daily interest so high?
A high daily figure usually reflects either a large balance or a high interest rate (or both). Personal loans and credit cards typically carry rates of 10–22%, while home loans are lower. Check whether your rate is competitive using current market data — if your rate is above 15%, it may be worth refinancing or consolidating the debt.
Embed this calculator
Add this calculator to your website. Free to use with attribution.
The calculator will resize to fit your content area. Please keep the attribution link visible — replace YOUR_SITE with your domain so we can attribute traffic correctly.