20 Unyielding Intelligence Armor x 5 (at 20% health)
15 - Max Intelligence through SPECIAL perks
11.25 - Brain Bombs (Needed: Herbivore mutation, Strange in Numbers w/ mutated teammate, Live & Live 3) [60 minutes]
8 - Egghead Mutation (Needed: Strange in Numbers w/ mutated teammate)
5 - Berry Mentats [5 minutes / +5 minutes w/ Rank 3 Chem Fiend / +2.5 minutes w/ Biochem Mesh mod on Torso Armor]
5 - Rank 4 Legendary Perk Intelligence
4 - Casual Team Bonus (4 fully bonded teammates)
3 - Herd Mentality Mutation (Needed: Strange in Numbers w/ teammate)
3 - Rank 3 Night Person Perk (Only at night)
3 - Shielded Flannel Shirt and Jeans with Casual Shielded lining
2 - Intelligence Bobblehead [1 hour / +1 hour w/ Curator]
2 - Mechanical Derby Game [30 minutes]
1 - Zeta Invaders [1 hour]
-1 → 0 - Marsupial Mutation Debuff with Rank 3 Class Freak Perk (0 if consuming Marsupial Serum for 1 Hour)
Leader Bobbleheads gives more bonus XP than Intelligence Bobblehead
Each point of Intelligence grants +2.072% XP based on Fallout Fandom Wiki.
Night time is 6:00 p.m. and 6:00 a.m.