Validity period specifies the time when SMS expires. If SMS is nott delivered before that moment, it is discarded by Service Center. Validity-Period can be in three different format: Relative, Absolute and Enhanced. WCL supports only Relative format. In this format the TP-Validity-Period is in integer representation, giving the length of the validity period, counted from when the SMS is received by the Service Center. The representation of time is as follows:
| TP-VP value | Validity period value |
| 0 to 143 | (TP-VP + 1) * 5 minutes (i.e. 5 minutes intervals up to 12 hours) |
| 144 to 167 | 12 hours + ((TP-VP - 143) * 30 minutes) |
| 168 to 196 | (TP-VP - 166) * 1 day |
| 197 to 255 | (TP-VP - 192) * 1 week |
