In the Philippine labor landscape, the 13th-month pay is a mandatory benefit that provides significant financial relief to employees at the end of the calendar year. However, when an employee suffers from an illness and claims Social Security System (SSS) sickness benefits, questions often arise regarding how these benefits—and the resulting absences—affect the final calculation of their 13th-month pay.

Legal Foundation of 13th Month Pay

Presidential Decree No. 851 (The 13th-Month Pay Law) mandates all employers to pay their rank-and-file employees a 13th-month pay, regardless of the nature of their employment, provided they have worked for at least one month during the calendar year.

The mathematical formula for the 13th-month pay is:

$$\text{13th Month Pay} = \frac{\text{Total Basic Salary Earned within a Calendar Year}}{12}$$

Definition of "Basic Salary"

Under the law, "basic salary" includes all remunerations or earnings paid by an employer to an employee for services rendered. It typically excludes:

Overtime pay
Profit-sharing payments
Night shift differentials
Holiday pay
Allowances and monetary benefits not considered part of the regular or basic salary

Nature of SSS Sickness Benefits

The SSS Sickness Benefit is a daily cash allowance paid to a member for the number of days they are unable to work due to sickness or injury. It is important to distinguish this from regular wages:

Social Security Grant: It is a benefit provided by the social insurance program, not a salary paid by the employer in exchange for labor.
Employer Role: While the employer usually advances the payment to the employee, the SSS subsequently reimburses the employer 100% of the amount paid.
Tax Status: Unlike basic salary, SSS benefits are generally exempt from income tax and withholding.

The Intersection: Why SSS Benefits are Excluded

The core conflict lies in the definition of "services rendered." Because 13th-month pay is calculated based on the basic salary earned for work performed, periods where an employee is not working do not contribute to the "Total Basic Salary" pool.

1. Exclusion from the Numerator

Since SSS Sickness Benefits are not considered "salary" or "wages" paid by the employer for services rendered, they are excluded from the computation of the total basic salary. When an employee is on Sickness Notification, they are technically on a "leave without pay" from the employer's perspective, even though they are receiving a cash allowance from the SSS.

2. Pro-rated Reduction

If an employee is absent for a month due to illness and receives SSS Sickness Benefits for that period, that month’s basic salary is essentially zero. Consequently, when the total annual salary is divided by 12, the resulting 13th-month pay will be lower than if the employee had worked the full year.

Legal Note: The principle of "A Fair Day's Wage for a Fair Day's Labor" applies. If no service was rendered to the employer, no basic salary is earned for that period, and thus no 13th-month pay accrues for that duration.

Illustrative Calculation

Consider an employee with a monthly basic salary of ₱20,000.

Scenario A (Full Attendance):
- Total Basic Salary: $₱20,000 \times 12 = ₱240,000$
- 13th Month Pay: $₱240,000 / 12 = \mathbf{₱20,000}$
Scenario B (Two Months on SSS Sickness Benefit):
- The employee worked for 10 months and was on SSS Sickness Leave for 2 months.
- Total Basic Salary Earned: $₱20,000 \times 10 = ₱200,000$
- 13th Month Pay: $₱200,000 / 12 = \mathbf{₱16,666.67}$

In Scenario B, the SSS Sickness Benefits received during those two months are not added to the ₱200,000 total.

Important Exceptions and Considerations

While the law sets the minimum standard, certain factors can alter this calculation:

Company Policy or CBA: If a Collective Bargaining Agreement (CBA) or a long-standing company policy explicitly states that periods of sickness or SSS leave are included in the 13th-month pay calculation, the employer is bound by that more favorable provision.
Paid Sick Leaves: If an employee uses their company-provided paid sick leaves (VL/SL), the pay received is considered part of the basic salary because it is a paid leave provided by the employer. In this case, the 13th-month pay remains unaffected. The SSS Sickness Benefit usually only kicks in once company-paid leaves are exhausted.
Non-Diminution of Benefits: If an employer has traditionally included SSS sickness periods in the 13th-month pay calculation for many years, they may be prohibited from stopping this practice under the Principle of Non-Diminution of Benefits.

Summary Table

Compensation Type	Included in 13th Month?	Reason
Regular Monthly Salary	Yes	Payment for services rendered.
Company Paid Sick Leave	Yes	Considered part of basic earnings.
SSS Sickness Benefit	No	Social security grant; not a salary.
Maternity/Paternity Benefit	No	Social security grant; not a salary.
Unpaid Medical Leave	No	No basic salary earned during this period.