it depends on the situation. it could be:
30 days/1 month - 100 pesos is good for 1 month
or
If you have another sim, pwede mong ipasaload kung malapit ng mag expire.
so kung may 100 pesos ka now good for 1 month, kung malapit ng 1 month ipasa mo sa other sim ang 99 pesos, it's good for another month. kung malapit na rin ang expiry, pasa mo back to the original sim ang 98, that's another 1 month.... repeat the process...
*remember:
1-10 pesos load = 3 days validity
11-50 pesos load = 15 days validity
51-100 pesos load = 30 days validity