If you are a self-employed or a voluntary member, the prescribed schedule of payment is also being followed, (depending on the 10th (last digit) of the SE/VM SS number). However, the frequency of contribution payments for self-employed or a voluntary member can be on a monthly or quarterly basis. A quarter covers three (3) consecutive calendar months ending on the last day of March, June, September and December. Any payment for one, two or all months for a calendar quarter may be made.
For OFWs
Payment of contributions for the months of January to December of a given year may be paid within the same year; contributions for the months of October to December of a given year may also be paid on or before the 31st of January of the succeeding year.
SOURCE: (SSS website)