Brihat Parashara Hora Shastra
स्वायुषो लग्नगे सूर्ये मङ्गले च शनैश्चरे । तदर्धं शुभसंदृष्टे पातयेद् द्विजसत्तम ॥ १३॥
The years etc. so arrived be deducted from the respective contribution, which will be the net span, donated by the Grah. If there is benefic‟s Drishti on Lagn, containing malefics, then the loss is only half.
english translation
svAyuSo lagnage sUrye maGgale ca zanaizcare । tadardhaM zubhasaMdRSTe pAtayed dvijasattama ॥ 13॥
hk transliteration by Sanscript