Fallout 4’s location is straightforward, but modded restoration is not. A base .fos file can reference content from plugins, and F4SE can add a paired cosave. The safest archive therefore includes the full save directory plus enough information to rebuild the mod environment. A failed load after moving PCs is not automatically evidence of file corruption; missing plugins, changed load order, or an absent cosave can be the real cause.
Choose the correct backup boundary
For Fallout 4, the researched PC save location is Windows: %USERPROFILE%DocumentsMy GamesFallout4Saves | Linux / Steam Play: Steam Play: <SteamLibrary-folder>/steamapps/compatdata/377160/pfx/. The known save file or folder pattern is *.fos
*.f4se (when created by F4SE). Copy the complete Saves directory. On F4SE setups, keep matching .fos and .f4se files together and record the installed mod/load-order state. Copying the complete documented save boundary is safer than selecting one visually obvious file, because companion metadata, indexes, backups, or multiple slots can be required together.
Make an offline copy before changing anything
Close the game first, wait for the active launcher to finish writing, then copy the save data to a separate folder that the game and sync client do not watch. Label the copy with the game, storefront, profile, and date. Documented launcher context: Steam, Microsoft Store / Xbox app. The standard Documents path is the primary Windows reference. Microsoft Store packaging can differ, so locate the active edition before restoring a file.
Account for cloud saves
Cloud behavior depends on storefront. OneDrive may also synchronize the Documents tree if Windows folder backup is enabled. Before restoring an older backup, decide which copy should win. If the game or launcher starts while an older manual copy is in place, synchronization can replace it before you confirm that it works. Keep the untouched backup outside the live save path until the restored progress has been opened and saved normally.
Restore without changing format assumptions
Base Fallout 4 saves use .fos. F4SE-enabled installations can create companion .f4se cosaves; preserving only one side of a modded save may remove script-extender state. Compatibility note: A clean base-game save and a heavily modded save have very different restoration requirements even if both use .fos. Restore into the matching storefront/profile context whenever possible. Do not rename a save extension, move a folder into a different container type, or assume a console/mobile copy is equivalent unless a tested migration path specifically says so.
Recovery fallback
If an apparently valid save crashes on load after migration, verify missing plugins and script-extender dependencies before replacing more files. Also check whether Documents is redirected by OneDrive. If the restored copy fails, put the untouched original back first. Then compare location, account/profile, cloud state, and the full directory structure before trying a different backup. The objective is reversible recovery, not repeated destructive experiments on the only copy.
Verification context: The standard Windows and Steam Play save locations were reviewed against current PCGamingWiki coverage. Format notes distinguish base .fos saves from optional F4SE cosaves.