Fallout 4 Survival Mode Guide: Saves, Disease, Weight

Short answer: three things define Survival mode in Fallout 4. You can only save by sleeping in a bed, on a mattress or in a sleeping bag; autosave and manual saves are disabled. Fast travel is off. And once you have enabled Survival and then switch it off, that save can never turn it back on. This guide covers those three, then the systems that actually kill characters: needs (hunger, thirst, sleep), disease, overencumbrance and the Adrenaline perk.

On sources. Numbers and rules follow Nukapedia, the community wiki. This article is not based on in-game testing. Where Nukapedia flags a value as approximate or incomplete, the text says so. Platform build numbers are not listed in official announcements, so no version number is asserted here.

Decide first: it is one-way, and what the name used to mean

Survival is chosen in the options menu. Nukapedia says it can be set before a new game, and Bethesda Support says you can load an existing save and pick it under Settings > Gameplay, so you can enable it at the start or later. It is not a toggle: once enabled, turning it off means that save cannot re-enable it. Weigh that before dropping the difficulty to escape a bug or a dead end. Console commands are also disabled while it is on.

The release history is recorded inconsistently. Nukapedia's Survival page says it was added on 29 March 2016, while its patch 1.5 page gives 28 April 2016 for PC and 6 May 2016 for Xbox One and PS4. Survival went through a beta period before shipping in 1.5, so 29 March reads best as the beta date (press coverage also describes the move out of beta). Also note that the difficulty previously called "Survival" was renamed "Very Hard", so older guides that say "Survival" may mean Very Hard.

Survival versus normal difficulty

Navigation changes too. The compass only detects locations within a few yards, and NPCs, friendly or hostile, no longer appear on it (quest-target enemies still do).

Saving by sleep: how it works and what it costs

Sleeping at least one game hour saves the game. Beyond that it only triggers a disease check. Sleeping two hours or more heals crippled limbs, restores Health progressively and starts reducing sleep fatigue. Cancelling out of the sleep prompt immediately (zero hours) still saves and still runs the disease check, but gives no healing or fatigue reduction.

Sleeping bags and mattresses can stop sleep fatigue building, but cannot clear it once you have it. On long outings, sleep early and briefly to save. The sleep timer runs about 14 game hours after a full rest, and each time you enter combat it advances by 15 minutes (with a cooldown, so rapid repeats do not stack).

Two traps

• Every sleep triggers one disease check. Many short sleeps mean many checks. Eat and drink before you lie down
• Sleeping strips Adrenaline ranks. Sleeping 7 or more hours removes all of them (table below)

Needs: hunger, thirst and sleep

According to Nukapedia, both hunger and thirst worsen through five stages from the satisfied state, each lowering SPECIAL.

Nukapedia marks the timing of each stage as approximate and incomplete. As a planning figure, it says you need about 9 drinkable items per game day (two per four awake hours, one per eight hours asleep). Carry more food and water than feels necessary.

How food and drink behave

• While hungry, the healing and bonuses of normal food are suppressed until you are Well Fed, so buff meals are wasted if you are still hungry
• The wiki advises clearing hunger with cheap food and saving expensive meals for their buffs (eating two items of any value is enough to clear a hunger stage)
• Drinking water heals 1.5 Health instead of 15, and only when you have no thirst status
• Nuka-Cola quenches only 40% of what its value implies and raises hunger. It delays sleepiness but does not replace water
• Stimpaks, RadAway and chems raise thirst or hunger. Antibiotics add thirst too (37.5 points)

Disease: risk builds up and is rolled when you sleep

There are seven diseases, and only mole rat disease (a permanent −10 max Health from a Vault 81 mole rat bite) can occur outside Survival.

Nukapedia's Fallout 4 diseases page lists what adds to the disease risk pool:

The pool drains 1% per game hour and starts rolling for disease once it reaches 25%. A suppressed immune system (from RadAway, for example) raises the risk; Nukapedia gives this as both "+20%" and "x120%", so the exact figure cannot be stated. After catching a disease you get a 24-hour grace period.

Four rules that matter in play:

1. Be fed and hydrated just before you sleep. Higher fatigue means higher risk
2. Herbal remedies prevent; they do not cure. Take one within one game hour of the check (sleeping or a high-risk event). It lowers the chance of the diseases it covers by 20%
3. Cure with antibiotics or a doctor. Paying a doctor to cure your health restores full Health and clears all diseases with no side effects
4. Avoid raw meat, dirty water and chems. High-risk actions trigger a roll immediately

Antibiotics are crafted at a chemistry station with Chemist rank 1 (INT 7, level 1) (2 Acid, 3 Glowing fungus, 2 Purified water, 3 Stimpak). They also turn up in first aid boxes and yellow chem boxes, and merchants and doctors sell them. Nukapedia notes that Herbal anodyne and Herbal stimulant may be impossible to craft because of a bug with harvesting Wild razorgrain.

Overencumbrance causes the most accidents

Ammo is weightless on normal difficulty but has weight in Survival. When overencumbered you suffer −2 Agility and Endurance, fatigue and periodic injury (legs can be crippled). Companions' safe carry weight is lower too.

• Strong Back (STR 6) rank 4 (level 30) stops the injury while overencumbered. On normal difficulty that rank allows fast travel; in Survival there is none, so it gives this protection instead. Rank 3 (level 20) lets you run on AP while overencumbered
• Adamantium Skeleton (END 7) ranks 1/2/3 (levels 1/13/26) cut limb damage by 30%/60%/100%. It does not stop the periodic damage from overencumbrance, so use Strong Back for that

Crippled limbs do not heal by themselves. Fix them with a Stimpak, a doctor or two or more hours of sleep.

Combat: double damage taken, and Adrenaline

Nukapedia's combat section says relative to Very Hard, your outgoing damage is x1.5 and incoming damage is x2.0 (both before damage resistance). The same page's summary table instead says you deal Hard-level damage and take double that, so the two statements do not agree on the baseline. Treat the multipliers as a rough guide; stronger enemies also appear sooner than on normal, so plan fights around not being hit.

The rewards are 2x experience from enemies and the automatic perk Adrenaline:

• Every 5 kills adds a rank worth +5% damage, up to rank 10 (50 kills) for +50%
• Sleeping removes ranks: 2 ranks for 1 hour, 8 ranks for 6 hours, and all ranks at 7 or more hours

Saving with short sleeping-bag naps therefore costs you little Adrenaline. After a long bed sleep your damage is back to base, so enter the next fight carefully.

Companions and settlements

• Downed companions do not get back up after combat. Heal them with a Stimpak or they return to their most recent settlement
• Robot companions (such as Automatron robots) must be repaired with a robot repair kit when downed. If left unattended they are destroyed instead of returning to a settlement. With the DLC, Codsworth also needs a robot repair kit to heal
• Workshop storage capacity shrinks, so settlement food and water output can suffer; do not stockpile

Build and gear notes for Survival

This is a sample allocation worked backwards from the perk requirements. Nukapedia states only the perk requirements; the spread below is this site's own example (starting SPECIAL totals 28 points).

6+7+5+3+3+2+2 = 28, with no stat below 1. This is one example, not the only workable spread.

You earn one perk point per level, so the table below is a suggested order, not a set you can take all at once. Levels are each rank's minimum requirement; you can take it at that level or later.

Starting END is 5, so you need two more points of Endurance to reach Adamantium Skeleton (level-up allocation, bobbleheads and so on). Until then rows 4, 5 and 7 are unavailable.

• Weapons and ammo: ammo weight varies widely (10mm round 0.025 versus 12 for a single mini nuke). Make a weapon that uses light ammo such as 10mm your main, and carry heavy rounds like mini nukes sparingly
• Armor: Nukapedia has no Survival-specific armor ratings, so this article recommends none. Power-armor builds are left to this site's other build guides
• Companions: Codsworth needs a robot repair kit to heal if Automatron is installed, and generic robots built with Automatron must be repaired with a kit when downed or they are destroyed. Humanoid companions do not get up, so bring Stimpaks for them. No companion is a pack mule, since their safe carry weight is lower

Early game to late game

1. Early (first day): plan for STR 6 so Strong Back is reachable, and do not hoard ammo or heavy weapons
2. Secure sleeping spots (bed, mattress, bag) at home and along expedition routes. Each one is a save point and a retreat line
3. Take Chemist (needs INT 7) for antibiotics. Until your INT is high enough, rely on merchants, doctors and first aid boxes
4. Always carry purified water and cooked food. Treat raw meat and dirty water as a last resort
5. Mid game (levels 10 to 25): take Strong Back ranks 2 and 3 and Adamantium Skeleton rank 2, and add beds and settlements as save points for expeditions
6. Late game (level 26+): Adamantium Skeleton rank 3 and Strong Back rank 4 nearly remove limb and weight accidents
7. Avoid long sleeps before a fight (1 hour costs 2 Adrenaline ranks, 7+ hours costs all of them). Save long sleeps for after combat

Summary

• Survival is chosen in the options menu (existing saves work too) and cannot be re-enabled after you turn it off. The old "Survival" difficulty was renamed Very Hard
• Saves happen only by sleeping (1+ game hour); no fast travel. Bag 3 hours, mattress 5, bed uncapped
• Hunger and thirst lower SPECIAL in five stages; Nukapedia flags the timings as approximate
• For disease: eat and drink before sleeping, take herbal remedies within one game hour of the check, and cure with antibiotics or a doctor
• Overencumbrance injury is stopped by Strong Back rank 4; Adamantium Skeleton does not cover it
• Adrenaline gives +5% per 5 kills up to +50%, and 7+ hours of sleep removes all of it
• Where Nukapedia contradicts itself (such as the damage baseline) this article calls the figure a rough guide

Sources (Nukapedia is a community wiki): Nukapedia — Survival mode, Nukapedia — Fallout 4 diseases, Nukapedia — Antibiotics, Nukapedia — Adrenaline, Nukapedia — Strong Back, Nukapedia — Adamantium Skeleton, Nukapedia — Hunger and Thirst, and Nukapedia — Fallout 4 patch 1.5 for the release dates.