Explainer · what is a bak file in autocad
What is a .bak file in AutoCAD?
By Saumyajit Maity · Published 27 Sept 2025 · Updated 27 Sept 2025
Look in the folder next to your DWG and you'll often spot a file with the same name but a .bak extension. It's easy to ignore — until the day your drawing corrupts, gets overwritten, or won't open, and that quiet little .bak file turns out to be the thing that saves your afternoon. A BAK file is AutoCAD's automatic backup of the previous saved state of your drawing, and knowing how to use it is one of those small skills that occasionally rescues hours of work.
This page explains exactly what a .bak file is, when AutoCAD creates it, how to recover a drawing from one, and how it differs from the autosave SV$ file that does a related but distinct job. None of it is complicated — but it's worth understanding before you need it rather than during a panic.
What a .bak file actually is
A BAK file is a backup copy of your drawing as it was at the previous save. By default, every time you save a DWG, AutoCAD takes what was the current saved version, renames it with a .bak extension, and then writes your new save as the .dwg. So at any moment, the .dwg holds your latest save and the matching .bak holds the save before it.
That means a .bak is a genuine, complete copy of your drawing — just one save behind. It's not a fragment or a log; it's the whole file. If your current DWG goes wrong, the .bak is a full, openable drawing you can fall back to. This is controlled by the ISAVEBAK system variable, which is on by default precisely because this safety net is worth having.
When AutoCAD creates one
AutoCAD creates or refreshes the .bak each time you save the drawing (with the backup feature enabled). The first save of a brand-new drawing may not produce one, because there's no previous version to preserve yet — but from the second save onward, you'll have a .bak that always trails your .dwg by exactly one save.
The .bak lives in the same folder as the .dwg by default and shares its base name, so MyPlan.dwg sits beside MyPlan.bak. Because it's tied to your manual saves, the .bak reflects how often you save: save frequently and your .bak is never far behind; go a long stretch without saving and the .bak could be well out of date. It's a one-step-back safety net, not a running history.
How to recover a drawing from a .bak
Recovering from a .bak is refreshingly simple: AutoCAD can't open a .bak directly, so you turn it back into a DWG by renaming it. Make a copy of the .bak first (so you don't lose it if something goes wrong), then rename the copy's extension from .bak to .dwg — for example MyPlan.bak becomes MyPlan-recovered.dwg. Give it a slightly different name so you don't overwrite your current file.
Then open that newly-named .dwg in AutoCAD and you're looking at your drawing as it was one save ago. Note that Windows hides file extensions by default, so you may need to enable "File name extensions" in File Explorer's View options before you can change .bak to .dwg. That single rename is the whole recovery trick.
BAK versus SV$ autosave
AutoCAD has a second safety net that people often confuse with the .bak: the autosave file, with an .sv$ extension. They solve overlapping problems differently. The .bak is created on your manual saves and holds the previous saved version. The .sv$ is created automatically on a timer (the SAVETIME interval, often every few minutes) and holds a snapshot taken between your manual saves.
That distinction matters when something goes wrong. If AutoCAD crashes before you've saved recent work, the .sv$ autosave may hold a more recent snapshot than the .bak, because it ran on the clock rather than waiting for you to hit save. To recover an .sv$, you also rename it to .dwg (it's usually in a temp folder you can locate via the OPTIONS dialog). Think of .bak as "the last good save" and .sv$ as "the most recent timed snapshot" — and when recovering, check both.
Managing .bak files (and turning them off)
Some people find .bak files clutter their project folders, since every drawing spawns one. You can control the behaviour: the ISAVEBAK system variable turns the backup on (1) or off (0). Turning it off stops the clutter but removes the safety net, so it's a trade-off most people decide isn't worth making — a stray file is cheap insurance against a lost day.
If you keep them, just don't treat the .bak as your only backup. It's only ever one save behind and lives in the same folder, so it won't help if the whole folder is lost or the drive fails. Real backup — versioned copies stored elsewhere or in the cloud — is still your job. The .bak is a quick in-place undo for a bad save or a corrupt file, not a substitute for a proper backup strategy.
Other recovery tools worth knowing
The .bak and .sv$ are your first line of defence, but AutoCAD has more for genuinely damaged files. The RECOVER command opens a problem DWG and runs an audit to repair what it can, which often rescues a file that won't open normally. AUDIT does a similar integrity check and fixes on a drawing that's already open. The DRAWING RECOVERY MANAGER appears after a crash and lists the files AutoCAD can attempt to restore, including autosave snapshots.
For the everyday "I just overwrote or corrupted my drawing" case, though, the humble .bak is usually the fastest fix: copy it, rename it to .dwg, open it, and you're back to your last good save. Knowing that one trick — and that the .sv$ autosave sits alongside it for crash recovery — covers the vast majority of situations where you'd otherwise fear you'd lost your work.
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Questions
Frequently asked
What is a .bak file in AutoCAD?+
A .bak file is AutoCAD's automatic backup of your drawing's previous saved state. Each time you save, AutoCAD renames the old saved version to .bak before writing the new .dwg, so the .bak is a full copy of your drawing from one save ago.
How do I open a .bak file?+
AutoCAD can't open a .bak directly. Copy the .bak, rename the copy's extension from .bak to .dwg (giving it a new name so you don't overwrite your current file), then open that .dwg in AutoCAD.
What's the difference between a .bak and an .sv$ file?+
A .bak is created when you manually save and holds the previous saved version. An .sv$ is an autosave created automatically on a timer between saves. After a crash, the .sv$ may hold more recent work — check both, and rename either to .dwg to recover.
Can I stop AutoCAD creating .bak files?+
Yes. Set the ISAVEBAK system variable to 0 to stop creating backups. It's on by default for good reason, though — the .bak is cheap insurance against a bad save, so most users leave it enabled despite the extra files.
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