In the Philippine jurisdiction, the social security system is bifurcated into two primary institutions: the Social Security System (SSS), which mandates coverage for private-sector employees, and the Government Service Insurance System (GSIS), which provides for employees in the public sector. While both serve the constitutional mandate of providing social justice and protection against the hazards of disability, old age, and death, their computation metrics and benefit structures differ significantly under the law.

I. The Social Security System (SSS) Pension Dynamics

The retirement benefits for private-sector workers are primarily governed by Republic Act No. 11199, or the Social Security Act of 2018. The monthly pension is not a flat rate but a variable figure determined by three distinct formulas, with the member receiving the highest resulting amount.

Key Determinants for SSS Computation

Credited Years of Service (CYS): This refers to the total number of monthly contributions paid. A minimum of 120 monthly contributions (10 years) is required to qualify for a lifetime monthly pension.
Average Monthly Salary Credit (AMSC): This is the average of the last 60 monthly salary credits (MSCs) prior to the semester of retirement, or the average of all MSCs paid, whichever is higher.
The "PHP 300 + 20% + 2%" Formula: The most common computation follows this structure:

Factors That Increase or Decrease SSS Benefits

Salary Credit Ceiling: The SSS implements a maximum MSC (currently being adjusted upward annually per RA 11199). Contributions based on a higher MSC lead to a higher AMSC, directly increasing the pension.
Early vs. Late Retirement: While optional retirement begins at age 60, mandatory retirement is at age 65. Continuing to contribute between 60 and 65 increases the CYS and potentially the AMSC.
Dependents’ Allowance: The pension increases by 10% of the monthly pension or PHP 250, whichever is higher, for each qualified minor child (up to five), beginning from the oldest.

II. The Government Service Insurance System (GSIS) Pension Dynamics

GSIS retirement is primarily governed by Republic Act No. 8291 (The GSIS Act of 1997). Unlike the SSS, GSIS benefits are more heavily weighted toward the length of service and the highest salary attained.

The Basic Monthly Pension (BMP) Formula

The BMP is calculated as follows:

37.5% of the Average Monthly Compensation (AMC) for those with 15 years of service.
An additional 2.5% of the AMC for every year of service in excess of 15 years.
The total BMP cannot exceed 90% of the AMC.

Key Determinants for GSIS Computation

Average Monthly Compensation (AMC): This is the average salary received during the last 36 months of service. For those with less than 36 months of total service, the actual average is used.
Period with Paid Premiums (PPP): This is the total number of months the member and the government agency paid premiums. Unlike the SSS, the GSIS requires at least 15 years of service to qualify for a pension.
Retirement Mode: Members may choose between:
5-Year Lump Sum: 60 months of pension paid in advance at retirement, with the regular monthly pension starting after five years.
Cash Payment and Pension: A smaller lump sum (18 months) plus immediate monthly pension.

III. Common Comparative Factors Affecting Both Systems

1. Outstanding Loan Balances

A critical factor that often diminishes the actual take-home benefit is the "deduction at source" policy. Under both SSS and GSIS laws, any outstanding salary, housing, or emergency loans—including accrued interest—are deducted from the retirement lump sum or the initial pension payments.

2. Re-employment and Pension Suspension

SSS: If a retiree under age 65 resumes employment or self-employment and earns an income, the monthly pension is suspended until they reach age 65 or cease employment again.
GSIS: If a retiree re-enters government service, the payment of the pension is generally suspended, as one cannot receive both a salary and a pension from the same sovereign fund simultaneously.

3. Survivorship and Beneficiaries

The "benefit" extends beyond the life of the member.

Primary Beneficiaries: Legitimate spouses (until remarriage) and minor/incapacitated children.
Effect on Computation: If the member dies, the primary beneficiaries typically receive 80% (for SSS) or 50% to 100% (for GSIS, depending on the mode) of the member's pension.

IV. Legal Limitations and Minimums

The law provides a "floor" to ensure a basic standard of living:

SSS Minimum Pension: PHP 1,200 for members with at least 10 CYS; PHP 2,400 for those with 20 CYS.
GSIS Minimum Pension: Currently pegged at PHP 5,000 under existing board resolutions and administrative directives to align with inflationary pressures.

V. Summary Table of Benefit Factors

Factor	SSS (RA 11199)	GSIS (RA 8291)
Min. Years for Pension	10 years (120 months)	15 years
Key Base Variable	AMSC (Last 60 months)	AMC (Last 36 months)
Max. Limit	Based on MSC ceiling	90% of AMC
Lump Sum Option	Generally 18 months (optional)	60 months (standard)
Dependent Bonus	Yes (10% per child, max 5)	Integrated into survivorship

In conclusion, the computation of Philippine pensions is a strict mathematical function of tenure (length of service) and contributions (salary credits). For both SSS and GSIS members, the most effective way to maximize benefits is to ensure the consistency of contributions and to minimize or settle outstanding loans prior to the date of retirement.