How to compute 13th month pay for 6 months?

13th month pay for 6 months of service is prorated: add up the total basic salary earned during those 6 months, then divide by 12, never by 6. For example, ₱90,000 in total basic salary over 6 months gives you ₱7,500 (₱90,000 ÷ 12). The same method covers 3, 4, and 5 months of service.