At the bottom of the squat your pelvis tucks under and your lower back rounds, often only in the last few inches of depth.
Squat to just above where the wink starts
Find your actual depth by filming from the side. Training a clean range beats forcing a range you cannot control.
Experiment with stance width and toe angle
Small changes often buy real depth immediately. This is the highest-leverage fix and costs nothing.
Brace properly before you descend
Big breath into the belly, brace like you are about to be punched, hold it through the rep.
Add hip flexor and adductor mobility work
Helps some people meaningfully and others barely at all, depending on whether the limit is soft tissue or bone.
The hardest part of fixing a form fault is that you cannot see yourself lift. Upload a video of your back squat and CleanerReps returns specific written corrections against a checklist built for that exact lift, usually in a couple of minutes.
Check your back squat formTwo free analyses, no card required. $19/month after that.