Day Count Actual360 calculator
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Day Count Actual360 calculator
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Formula: Interest = Principal × (Annual Rate / 360) × Actual Days
Worked example — Interest (Actual/360) = $7,986.11
Formula
Interest = Principal × (Annual Rate / 360) × Actual Days
The Actual/360 convention divides the annual interest rate by 360 to obtain the daily rate, then multiplies by the actual number of calendar days in the period. This produces a year fraction of Actual Days / 360, which is used as the accrual factor for interest calculations.
Worked Examples
Example 1: Commercial Loan Interest (6 Months)
Problem:Calculate interest on a $250,000 loan at 6.25% from March 1 to September 1 using Actual/360.
Solution:Actual days: March(31) + Apr(30) + May(31) + Jun(30) + Jul(31) + Aug(31) = 184 days Year fraction (Actual/360): 184 / 360 = 0.51111 Interest = $250,000 × 6.25% × 0.51111 = $7,986.11
Result:Interest (Actual/360) = $7,986.11
Example 2: Bond Accrued Interest Comparison
Problem:Compare accrued interest on a $1,000,000 bond at 4.5% from Jan 15 to Jul 15 using Actual/360 vs Actual/365.
Solution:Actual days: Jan(16) + Feb(29) + Mar(31) + Apr(30) + May(31) + Jun(30) + Jul(15) = 182 days Actual/360: $1,000,000 × 4.5% × 182/360 = $22,750.00 Actual/365: $1,000,000 × 4.5% × 182/365 = $22,438.36 Difference: $311.64 more under Actual/360
Result:Actual/360: $22,750 | Actual/365: $22,438.36 | Diff: $311.64
Frequently Asked Questions
What is the Actual/360 day count convention?
The Actual/360 day count convention calculates interest by dividing the actual number of days in a period by 360 days per year. This method is widely used for money market instruments, commercial loans, and LIBOR/SOFR-based floating rate products. Because it divides by 360 instead of the actual 365 or 366 days in a year, it effectively charges slightly more interest than an Actual/365 convention for the same annual rate. For every full calendar year, the borrower pays interest for 365/360 = 1.01389 year fractions, resulting in approximately 1.4% more interest than Actual/365. This makes Actual/360 more favorable to lenders.
What is the difference between Actual/360 and 30/360 day count conventions?
Actual/360 uses the real calendar number of days between two dates divided by 360, while 30/360 assumes every month has exactly 30 days and divides by 360. For example, from January 15 to February 15 is 31 actual days under Actual/360 but exactly 30 days under 30/360. The 30/360 convention (also called Bond Basis) is simpler to calculate and is commonly used for corporate and municipal bonds, while Actual/360 is standard for money markets, LIBOR-based loans, and many floating-rate instruments. The choice of convention can significantly impact interest amounts, especially over longer periods or with large principal amounts.
Why do banks use Actual/360 instead of Actual/365?
Banks prefer Actual/360 for commercial lending because it generates slightly higher interest income. When the annual rate is divided by 360 instead of 365, the daily rate is higher (e.g., 5% / 360 = 0.01389% vs. 5% / 365 = 0.01370% per day). Over a full 365-day year, this results in approximately 1.39% more interest collected. For a $1,000,000 loan at 5%, the difference is about $694 per year. This convention also aligns with the historical banking practice of using a 360-day year for simplified calculations. Regulators and courts have upheld this practice as standard, though borrowers should be aware of its effect on effective interest rates.
How does the Actual/360 convention affect mortgage calculations?
While residential mortgages typically use the Actual/365 or 30/360 convention, some commercial mortgages and adjustable-rate mortgages use Actual/360. This means the borrower pays interest on 365 days but the daily rate is calculated using a 360-day year, resulting in higher effective interest. For a $500,000 commercial mortgage at 6%, the annual interest using Actual/360 is approximately $30,416.67 (365 × $500,000 × 6% / 360) versus $30,000 using Actual/365, a difference of $416.67 per year. Over a 10-year loan term, this can add up to several thousand dollars in additional interest, making it important to verify which convention is specified in loan documents.
What is a year fraction and why does it matter in finance?
A year fraction (also called day count fraction or accrual factor) is the proportion of a year represented by a given time period, calculated according to a specific day count convention. It is the key multiplier used to compute interest: Interest = Principal × Annual Rate × Year Fraction. Different conventions produce different year fractions for the same date range. For example, 182 actual days equals 0.50556 using Actual/360, 0.49863 using Actual/365, and 0.50000 using 30/360. The choice of convention is specified in loan agreements, bond indentures, and ISDA documentation. Getting the year fraction wrong can lead to material discrepancies in settlement amounts and financial reporting.
References
Reviewed for accuracy by Daniel Agrici, Founder & Lead Developer · Editorial policy
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