Simple Interest by Day Count Calculator
Calculate simple interest over an exact number of days with a 360- or 365-day basis you choose.
Calculate simple interest over an exact number of days with a 360- or 365-day basis you choose. Example result: simple interest = $73.97. Compare your own inputs below. Estimates depend on the stated assumptions and are not a quote or forecast. Defaults are illustrative, not recommendations.
Your result
- Simple interest
- $73.97
- Principal plus interest
- $5,073.97
With the example inputs, simple interest is $73.97. Simple interest does not earn interest on prior interest. A shorter day-count denominator produces more interest for the same principal, rate and actual days.
How to use this simple interest by day count calculator
- Principal: enter the amount in your selected currency. The worked example uses $5,000.00.
- Annual simple interest rate: enter a percentage using 5 to mean 5%. The worked example uses 6%.
- Number of days: enter the quantity in days. The worked example uses 90 days.
- Day-count year basis: enter the quantity in days. The worked example uses 365 days.
Start with figures from the same statement date or planning period. Calculate once, save scenario A, then change one assumption to understand its effect. The comparison shows B minus A; a positive difference means the result increased, which is not automatically better.
Formula and calculation method
Interest = principal × annual rate × days / year basis.
The calculator evaluates this relationship directly in your browser. The displayed precision is for readability and does not imply a guaranteed outcome. Time periods and rate conventions matter: use the exact units in each input label and avoid mixing monthly and annual values.
What the result means
Simple interest does not earn interest on prior interest. A shorter day-count denominator produces more interest for the same principal, rate and actual days.
Two worked examples
1. Illustrative planning scenario
Principal = $5,000.00; Annual simple interest rate = 6%; Number of days = 90 days; Day-count year basis = 365 days.
Apply the stated formula with these inputs. Monetary examples use USD; percentages are divided by 100 inside the calculation. Intermediate calculations retain full precision and displayed amounts are rounded.
| Output | Calculated result |
|---|---|
| Simple interest | $73.97 |
| Principal plus interest | $5,073.97 |
2. Simplified calculation check
Principal = $1,000.00; Annual simple interest rate = 12%; Number of days = 90 days; Day-count year basis = 360 days.
Apply the stated formula with these inputs. Monetary examples use USD; percentages are divided by 100 inside the calculation. Intermediate calculations retain full precision and displayed amounts are rounded.
| Output | Calculated result |
|---|---|
| Simple interest | $30.00 |
| Principal plus interest | $1,030.00 |
The second example uses simpler inputs to make the arithmetic easier to check. It is also included in the automated regression suite. These examples illustrate the model and are not market averages, live offers or personalized advice.
Assumptions and limitations
Actual-days numerator only. Does not implement 30/360 date adjustment, leap-year actual/actual or compounding. Enter dates’ elapsed days separately.
Use this output to frame a question or compare consistent scenarios. Reconcile any decision involving an actual product, employment agreement or financial statement with its underlying documents. If a contract uses different rounding or timing, its result may differ from this estimate.
Frequently asked questions
Is actual/360 the same as 30/360?
No. Actual/360 uses elapsed calendar days; 30/360 also adjusts the day count based on contractual month conventions.
How do I interpret the simple interest result?
Simple interest does not earn interest on prior interest. A shorter day-count denominator produces more interest for the same principal, rate and actual days.
What assumptions can change this estimate?
Actual-days numerator only. Does not implement 30/360 date adjustment, leap-year actual/actual or compounding. Enter dates’ elapsed days separately.
Can I compare two scenarios without creating an account?
Yes. Save scenario A, change one or more inputs to create scenario B, and compare each result with its difference. Neither scenario requires an account.
Can I use this calculator in another currency?
Yes. Select a display currency and enter every monetary input in that currency. This changes formatting only; it does not convert exchange rates or apply local laws. The static worked examples are in USD.
Sources and verification
The following primary sources provide background on the financial concepts. CalcPane’s formula and assumptions above define this specific model; these organizations do not endorse CalcPane or certify its outputs.
Formula implementation and worked examples checked by automated tests on 2026-10-17. Inspect this calculator’s inputs and expected outputs. Read our calculation methodology. Independent professional review has not been completed for this release.
Use this calculator on your website
Let your visitors explore their own numbers with this free browser-based embed. Adjust the iframe height to suit your page. A public embed includes visible CalcPane attribution.
Explore website calculators · See Pro and Business plans · Ask about installation
Cite this calculator
CalcPane. (2026-10-17). Simple Interest by Day Count Calculator. https://calcpane.com/simple-interest-day-count-calculator/
Related calculators
- CD Early Withdrawal Penalty Calculator
- APR to APY Compounding Calculator
- Multiple Sinking Funds Monthly Budget Calculator
- Related original CalcPane calculator
All saving and banking calculators · Complete calculator directory