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Input annual or monthly interest rate to quickly calculate daily interest rate, daily interest, and total interest.
The daily interest rate as a decimal. For example, 0.05 represents 0.05% daily interest.
Enter principal, daily rate, and term to calculate interest.
Overview
Understand what the tool solves, how it works, and the boundaries of its data.
This calculator estimates simple interest from three values: principal, a daily interest rate, and a term. Enter the rate as a percentage number: for example, 0.05 means 0.05% per day, or 0.0005 as a decimal multiplier. The principal can be expressed in any currency or amount unit, and the result uses that same unit. No currency conversion is performed.
Daily interest = principal × daily rate (%) ÷ 100
Total interest = daily interest × term in days
Amount at end of term = principal + total interest
Monthly rate equivalent = daily rate (%) × 30
Annual rate equivalent = daily rate (%) × 365
The principal stays unchanged for every day in this model, so interest does not earn additional interest. A month is treated as 30 days and a year as 365 days for term conversion. These are calculator conventions: a term of 2 months becomes 60 days, and 1 year becomes 365 days. The displayed monthly and annual rates are straight-line equivalents of the daily percentage, not an effective yield or a lender's APR.
For a principal of 10,000 units, a daily rate of 0.05%, and a term of 30 days: daily interest is 10,000 × 0.05 ÷ 100 = 5 units. Total interest is 5 × 30 = 150 units, and the end amount is 10,150 units. The monthly equivalent shown is 1.50%, and the annual equivalent is 18.25%. The tool formats monetary-style result values to two decimal places; use the full formula when you need to inspect an unrounded intermediate.
Guide
Follow the workflow and verify inputs and outputs with practical examples.
Enter a positive balance or amount. Include no currency symbol; the result simply follows your chosen unit, such as dollars.
Type the rate as a percent value. Enter 0.05 for five-hundredths of one percent per day, not 0.0005 and not 5.
Enter a positive number and select days, months, or years. The calculator converts months at 30 days each and years at 365 days each.
Review total interest, daily interest, end amount, converted day count, and the simple monthly and annual rate equivalents. Reset clears the entries.
For a quick check, 1,000 at 0.1% per day for 10 days produces 1 unit of interest per day and 10 units total.
Use cases
See how the tool fits into real work and everyday tasks.
When a written agreement states a fixed daily percentage and unchanged principal, enter those terms to inspect the simple-interest amount over the planned number of days.
Keep the principal and daily rate the same, then try different day counts to see how simple interest changes in direct proportion to time.
Use a hypothetical balance to check the arithmetic in a quote or worksheet. Match the result unit to the input and compare each assumption with the document that governs the transaction.
Q&A
Find concise answers to common questions and confusing cases.
No. The input asks for a daily rate as a percentage value. Convert a rate to a daily figure using the convention in your agreement before entering it; this page does not infer or convert an annual input.
No. It applies the same principal for each day and multiplies the daily interest by the number of days. Previously accrued interest is not added to principal.
Each month is fixed at 30 days and each year at 365 days, regardless of calendar month lengths or leap years.
No. It is the daily percentage multiplied by 365. It does not represent a regulated APR, effective annual yield, fees, payment schedule, or a particular financial product's terms.
Notes
Review scope, result limitations, and important precautions before use.
This is a mathematical estimate using fixed principal, simple interest, a 30-day month, and a 365-day year. Real accounts or contracts can use changing balances, compounding, different day-count rules, fees, or rounding practices. The result is not a quote or a statement of the amount owed; check the applicable terms and obtain qualified financial guidance for decisions about borrowing or investing.
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