Which of the following is not a method commonly used by lenders to calculate interest?

Which of the following is not a method commonly used by lenders to calculate interest?

• A. 31/365
• B. Actual/360
• C. Actual/365
• D. 360/360

Answer: (A)

In lending, interest is tied to a day count convention, which turns actual days into a fraction of a year to apply the annual rate. The common conventions use actual days in the period divided by a denominator like 360 or 365, or they fix the denominator to 360 for both parts, so the interest math stays consistent across periods. Actual/360 and Actual/365 both use the actual number of days in the accrual period in the numerator, with the year length set to 360 or 365 in the denominator. 360/360 uses 360 days in both the numerator and denominator, simplifying monthly calculations. These are standard because they reflect real time but keep the math uniform. 31/365 isn't a recognized day-count convention. The numerator would imply counting a fixed 31 days for each period, which doesn't align with varying month lengths (some months have 30, some 31, and February has 28 or 29). Because it isn’t a standard, widely used method, it isn’t employed by lenders to calculate interest, even though you could mathematically plug in 31 days over 365 for a single period.

In lending, interest is tied to a day count convention, which turns actual days into a fraction of a year to apply the annual rate. The common conventions use actual days in the period divided by a denominator like 360 or 365, or they fix the denominator to 360 for both parts, so the interest math stays consistent across periods.

Actual/360 and Actual/365 both use the actual number of days in the accrual period in the numerator, with the year length set to 360 or 365 in the denominator. 360/360 uses 360 days in both the numerator and denominator, simplifying monthly calculations. These are standard because they reflect real time but keep the math uniform.

31/365 isn't a recognized day-count convention. The numerator would imply counting a fixed 31 days for each period, which doesn't align with varying month lengths (some months have 30, some 31, and February has 28 or 29). Because it isn’t a standard, widely used method, it isn’t employed by lenders to calculate interest, even though you could mathematically plug in 31 days over 365 for a single period.