Measure the post interface
With the vehicle manual and cover instructions beside you, record post spacing center-to-center, post diameter, slot shape, headrest width, adjustment range, and the distance from the post slots to the cover seams. Photograph the seat before removing anything.
The opening should let the headrest move as designed without forcing the cover across the posts. A cover that fits the cushion but traps the headrest is not a complete fit. Do not cut through a marked airbag seam or use a generic slot as permission to change the restraint system.
Limits
The two-impression, one-click Bing row is a small demand signal, not a product recommendation. No vehicle, cover, crash condition, or airbag deployment was tested.
Sources and related reading
See Also
If you want to move from general advice into actual product choices, start with Are Neoprene Seat Covers Hot? Material, Climate, and Ventilation Tradeoffs, Car Seat Cover Measurement: Headrest, Width, and Recline Clearance, and Canvas vs Neoprene Seat Covers: Which Constraint Matters First?.
For a wider picture after the basics, Overhead Console vs Seat Back Car Storage Organizers: Which One Fits Your Needs? and Best Breathable Car Seat Covers Under $80 for Comfort are the next places to read.