Saravali 39.2

39.2

tīna prakāra kā ( aṃśa, piṇḍa, nisarga ) āyu meṃ kaba kisakā grahaṇa
aṃśodbhavaṃ vilagnātpaiṇḍyaṃ bhānornisargajaṃ candrāt |
eteṣāṃ yo balavānekatamastasya kalpayedāyuḥ ||

When to take which of the three types of lifespan (aṃśa, piṇḍa, and nisarga):
The aṃśodbhava lifespan is from the ascendant, the paiṇḍya from the Sun, and the nisargaja from the Moon.
Whichever of these is the most powerful, one should determine the lifespan from that one.