Quick answer
Daily interest = balance × annual rate ÷ days in the year. $10,000 at 5% on a 365-day basis accrues $1.37 a day, $41.10 over 30 days and $500 over a year.
Enter the balance, annual rate and day-count basis. The calculator returns interest per day, per 30 days and per year.
Related tools: Simple Interest Calculator: Interest earned or owed without compounding. Compound Interest Calculator: Future value with compound interest and regular contributions. Real Interest Rate Calculator: Inflation-adjusted interest rate using the exact Fisher relation.
How to use the Interest Per Day Calculator
- Enter balance ($) (above 0).
- Enter annual rate (%) (between 0 and 100).
- Choose day-count basis: 365 days and 360 days.
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Balance | A number, in $ | > 0 |
| Annual rate | A number, in % | ≥ 0, ≤ 100 |
| Day-count basis | Choose one: 365 days; 360 days | Starts at 365 days |
Formula and method
Formula
daily interest = balance × rate ÷ days in year
IEEE-754 double precision; money shown to cents, rates to 4 decimals. Results are estimates, not financial advice.
Simple (non-compounding) daily accrual on the basis you choose.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Balance = 10000; Annual rate = 5; Day-count basis = 365 days.
| Result | Value |
|---|---|
| Interest per day | $1.37 |
| Per 30 days | $41.10 |
| Per 365 days | $500.00 |
Example 2
Inputs: Balance = 10000; Annual rate = 5; Day-count basis = 360 days.
| Result | Value |
|---|---|
| Interest per day | $1.39 |
| Per 30 days | $41.67 |
| Per 365 days | $506.94 |
Example 3
Inputs: Balance = 2500; Annual rate = 3.65; Day-count basis = 365 days.
| Result | Value |
|---|---|
| Interest per day | $0.25 |
| Per 30 days | $7.50 |
| Per 365 days | $91.25 |
The first line is the headline result (interest per day). Below it the interest Per Day Calculator lists per 30 days and per 365 days, which describe the same case from other angles. IEEE-754 double precision; money shown to cents, rates to 4 decimals. Results are estimates, not financial advice.
Day-count basis
A 360-day basis accrues slightly more per day ($1.39 instead of $1.37) and is common in commercial loans. Always check which basis your lender uses.
Simple interest
This is simple interest on a fixed balance. If interest compounds, the daily amount grows with the balance. Use it to check payoff quotes or the cost of a late payment.
How the result changes with balance
Holding every other input at the first worked example, this table changes only balance. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Balance | Interest per day | Per 30 days | Per 365 days |
|---|---|---|---|
| 5000 | $0.68 | $20.55 | $250.00 |
| 10000 | $1.37 | $41.10 | $500.00 |
| 20000 | $2.74 | $82.19 | $1,000.00 |
| 40000 | $5.48 | $164.38 | $2,000.00 |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Balance: entering "0" shows "Balance must be greater than 0." beside that field and no result.
- Annual rate: entering "-1" shows "Annual rate must be at least 0." beside that field and no result.
Choosing between the Interest Per Day Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Simple Interest Calculator](/finance/simple-interest-calculator/) | principal, annual rate and time | Interest |
| [Compound Interest Calculator](/finance/compound-interest-calculator/) | initial amount, annual interest rate and years | Future value |
| [Real Interest Rate Calculator](/finance/real-interest-rate-calculator/) | nominal interest rate and inflation rate | Real interest rate |
| [APY Calculator](/finance/apy-calculator/) | nominal annual rate and compounding | APY |
| [Continuous Compounding Calculator](/finance/continuous-compound/) | principal, annual rate and years | Future value |
Background: interest, saving and investing
A nominal rate (APR) does not include the effect of compounding; the annual percentage yield (APY) does: APY = (1 + r/n)^n − 1. A 5% nominal rate compounded annually is 5.000%, semi-annually about 5.063%, quarterly about 5.095% and monthly about 5.116%, so more frequent compounding helps, but with diminishing returns.
The rate you enter in a projection is an assumption, not a promise: real returns vary and can be negative. Fees and taxes are not modelled unless the page says so.
Assumptions and limitations
- A 360-day basis accrues slightly more per day
Results are estimates for planning, not financial advice. Lender terms, fees, taxes and rounding rules can change real figures, so confirm important numbers with your lender or a licensed adviser.
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for balance and annual rate to confirm this.
Frequently asked questions
How much interest on $1,000 at 3%?
At 3% a $1,000 balance accrues 1,000 × 0.03 ÷ 365 ≈ $0.082 a day.
What is 360-day basis?
Months of 30 days, year of 360.
Is it compounded?
No, this is simple interest.
What does the Interest Per Day Calculator calculate?
Daily interest on a balance at an annual rate. It returns Interest per day, Per 30 days and Per 365 days.
What formula does the Interest Per Day Calculator use?
daily interest = balance × rate ÷ days in year. Simple (non-compounding) daily accrual on the basis you choose.
What do I need to enter in the interest Per Day Calculator?
You enter Balance ($), Annual rate (%) and Day-count basis.
How is the result rounded or limited?
IEEE-754 double precision; money shown to cents, rates to 4 decimals. Results are estimates, not financial advice. A 360-day basis accrues slightly more per day.
What does the “Day-count basis” option change?
It sets how the interest Per Day is worked out. The choices are 365 days and 360 days.
What is an example of a interest Per Day result?
With balance 10000, annual rate 5 and day-count basis 365 days, the interest per day is $1.37.
Can I rely on this calculator for a decision?
Results are estimates for planning, not financial advice. Lender terms, fees, taxes and rounding rules can change real figures, so confirm important numbers with your lender or a licensed adviser. For this calculator in particular: A 360-day basis accrues slightly more per day.
Related calculators
- Simple Interest Calculator — Interest earned or owed without compounding.
- Compound Interest Calculator — Future value with compound interest and regular contributions.
- Real Interest Rate Calculator — Inflation-adjusted interest rate using the exact Fisher relation.
- APY Calculator — Convert a nominal rate (APR) into the effective annual yield (APY).
- Continuous Compounding Calculator — Growth with continuously compounded interest.
- Interest Rate Calculator — Annual interest rate implied by a loan amount, payment and term.
Sources
- Standard time-value-of-money relations (e.g. Brealey, Myers & Allen, Principles of Corporate Finance)
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.