Understanding the Term "Month"
The term "month" has several meanings.
As a stretch of a period of time from the perspective of a year, it is one of the twelve periods into which a year is divided, and therefore each would have 28, 29, or 31 days.
In commerce, it is a period of 30 successive days.
As a unit of time based on the revolution of the Moon around the Earth, it is the period between two successive new moons or an average of 29.53 days.
The length or duration of a month, therefore, is a matter of approximation for the purpose of convenience of calculation.
Payment Structure and Overtime Calculation
As per your post, your payment is for a month comprising 26 days, i.e., 26 working days plus 4 holidays in a month notionally comprising 30 days on average. In other words, the monthly wages/salary paid for 26 working days includes the 4 weekly off days. Since a week is considered to comprise 7 days, the principle of the 7th successive day after 6 days of continuous work as the weekly-off has emerged.
The universal practice of calculating overtime work is based on actual hours worked in excess of normal working hours, isn't it? So, compensation for overtime work is determined on the basis of the hourly rate only, and as such, the actual number of days in a particular month, in my opinion, is immaterial for the purpose of calculating overtime wages.
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