Fallout 4 has 275 SPECIAL related perks that would collectively require thousands of hours worth of experience (XP) if playing normally. Even if you’re not trying to truly 100% the game, having as many perks as possible can’t hurt and can make Fallout 4 more enjoyable if you hate being under-leveled at all. Fortunately, there are legitimate methods of power leveling without exploits or glitches. Those that require DLC will be noted for those that only have the base game.
(Actually) Max Out Intelligence
In Fallout 4, the Intelligence SPECIAL stat has increased the Sole Survivor’s rate of XP gain (as opposed to increasing Skill points upon level up like previous games), with an approximate increase of 3% XP gain for every point the Sole Survivor puts into Intelligence. This means that XP gain at Intelligence 1 is 103%, while XP gain at Intelligence 10 is 130%.
Normally in the Fallout series, SPECIAL stats have a set max limit of 10. This is why in previous games, experienced players raised SPECIAL stats to 9 at startup (or through leveling) and only raised it to 10 through the use of a bobblehead/implant as the benefit from the bobblehead/implant would otherwise be wasted if the SPECIAL stat was already at 10. Fallout 4 changed the SPECIAL system to allow SPECIAL stats beyond the base 10 shown in the perk menu. Intelligence beyond the base 10 has additional benefits to XP gain and can be raised to exorbitantly high levels through the use of certain armor and items (some of which can only be found as part of DLC content).
Without the use of chems, the Sole Survivor can have a near permanent 33 Intelligence SPECIAL stat through the following:
Max Base SPECIAL Stat – 10
You're SPECIAL! Magazine – 1
Intelligence Bobblehead – 1
Vault 88 Overseer Desk (Vault-Tec Workshop DLC) – 1
Fancy suit & tie (Nuka-World DLC) – 1
Unyielding Legendary armor (Far Harbor DLC) -15
Inquisitor’s Cowl (Far Harbor DLC) – 4
With the use of chems and other, non-permanent bonuses, the Sole Survivor can have an Intelligence SPECIAL stat of 46 through the following:
Night person Perk – 3
Berry Mentats – 5
Daddy-O – 3
X-Cell – 2
In the Nuka-World DLC, Intelligence can be boosted to the highest possible value of 82 with a one-time bonus from the Hubologists, which will temporarily increase Intelligence by 36.
With all possible Intelligence bonuses, the Sole Survivor’s XP gain should be 346%.
If you do not have DLC installed, without the use of chems, below is the highest possible Intelligence of 17.
Max Base SPECIAL Stat – 10
You're SPECIAL! Magazine – 1
Intelligence Bobblehead – 1
Press Cap – 1
Liam’s Glasses – 2
Lab Coat – 2
Absent any (almost game-breaking) Intelligence SPECIAL stat boosts described above, the BEST perk for increased XP gain is the (unfortunately named) Idiot Savant perk. The Idiot Savant perk bestows the Sole Survivor a random chance to gain an XP multiplier for any action, with the likelihood of Idiot Savant triggering being anchored to how low your Intelligence SPECIAL stat is. This means an action done with an Intelligence of 10 is less likely to have Idiot Savant trigger then an action done with an Intelligence of 1.
Reddit user Minusra conducted an experiment to empirically see what the highest possible XP gain was. Minusra concluded that Idiot Savant is ALWAYS worth taking due to the increased XP gain. As discussed in the Intelligence stat section above, an Intelligence of 10 has a 130% XP modifier, while Idiot Savant level 2 with an Intelligence of 1 has an XP modifier of 151%, the equivalent of having an Intelligence of 16 without Idiot Savant.
It must be noted that because of the fact this was before most DLCs came out, this does not take into account ridiculously high Intelligence stats like 46. As the likelihood of Idiot Savant triggering bottoms out at 1.66% at Intelligence of 11, it seems Idiot Savant is still worthwhile even at very high Intelligence levels.
If you want to look at the original post by Minusra, you can find it at the link found here.
Max Out XP Modifiers
Unlike Intelligence SPECIAL stat boosts, which apply across the board in every situation, many XP Modifiers only apply in very limited circumstances and are not viable as a long-term source of increased XP gain (which is why they have not been listed here). However, the most versatile XP Modifiers are listed below:
Quiet Reflection (5%)/Well Rested (10%)/Lover’s Embrace (15%)
Squirrel Stew (2%)
Live and Love Issue #10 (5% when traveling with a companion)
All things being equal, these are fairly easy to acquire as beds are plentiful for Well Rested/Lover’s Embrace, Squirrel Stew can be crafted in mass quantities, and all that’s need for Live and Love Issue #10 is a companion.
Perhaps the most obvious method of getting more levels. Play through the story. Not only do quests like the Nuclear Option present the largest possible XP opportunity, you’ll get loot otherwise unavailable like legendary weapons and armor. This, alongside all other XP “farming” method listed below, can be done in conjunction with all the Intelligence/XP Modifier bonuses listed above.
Abusing the settlement system is one early game strategy to get easy experience. Virtually every item that can be crafted at a workbench/crafting table grants XP, which can be especially lucrative when building large settlements.
Some players prefer to “skip” parts of the early game where they otherwise would be low-leveled by scrapping everything in Sanctuary and continually building low resource intensity items like fences or shelfs. Often, this can raise the Sole Survivor’s level to 10 before even leaving the starting area.
Crafting can still be beneficial at higher levels too. Not only is the Sole Survivor more likely to have the prerequisite perks to make late game items and mods, they will have more infrastructure for crafting more useful items that usually grant more XP. For example, after setting up a water purifier farm (one of the best sources of caps) and a crop farm, the Sole Survivor can farm adhesive too. Having the ability to buy many resources from venders also is a potential source of XP as those resources can be crafted into items to be resold for profit.
The Wasteland Workshop DLC introduced, amongst other things, functional cages that can capture wasteland creatures like deathclaws, supermutants, and ferocious cats. Of note is the gunner cage, which, despite its somewhat prohibitive construction cost of 500 caps each, can be massed collectively to create an XP/ammo/legendary farm. If one adds to the gunner cages a settlement with 0 defense and a high resource count (likely through water purifiers), that settlement will be attacked constantly, which increases the amount of enemies that can be killed off.
To turn gunner farming on/off, add defenses reliant on power like turrets that are connect to a power source you can turn on/off. Whenever the defenses are on, gunner farming is turned off. Gunners are preferable to other cage-able creatures like raiders as they spawn with better gear and are easier to kill en masse then enemies like deathclaws (which notably, will have a high amount of legendary spawns).
The XP gain from this can be increased through Idiot Savant level 3 (allowing 60 seconds with a three times XP multiplier) and Gage’s companion affinity perk (increasing XP gained by killing enemies by 5%).
The Wasteland Workshop DLC also has brahmin cages, which consistently trap brahmin for the purposes of creating fertilizer. Fertilizer can be crafted with plastic to create jet. Though this is inferior in terms of cap collection as compared to water purifier farms, jet farming still grants XP from crafting. If the Sole Survivor only wants jet for its own sake, they can finish the Nuka-World DLC and craft pick-me-up stations, which automatically creates buffout, jet, and psycho, with no limit on how many may be created.
This also possible without DLC (albeit slower) though brahmin feed troughs, which have a chance to attract brahmin to the settlement.
Radiant Quest Grinding
A consistent source of XP (depending on which faction the Sole Survivor is allied with) is grinding radiant quests for each faction, which are repeatable quests that have the Sole Survivor go to a specific location and usually kill an enemy or find a certain item.
The easiest radiant quests are likely those for the Brotherhood of Steel given how they only require a small task to be completed. For example, Cleansing the Commonwealth quests (given by Knight Rhys at the Cambridge Police Station) only require one enemy to be killed and Quartermastery quests (given by Scribe Haylen also at the Cambridge Police Station) only require one item to be collected. Afterwards, the Sole Survivor can easily just run away and fast travel.
An “exploit” is to grind the Learning Curve quest (given by Proctor Quinlan on the Prydwen), where the Sole Survivor sneak attacks the BoS scribe he was supposed to escort (which is the most appropriate response to all escort missions), which completes the quest as if it was completed normally.
Regardless, however many times you level up, there will always be another settlement that needs your help.