A good brake pedal feels firm and stops the car with a predictable amount of travel. When the pedal goes soft or spongy - sinking farther than normal or feeling squishy - the hydraulic system is trying to tell you something. This is a safety issue, so do not put it off.
Air in the brake lines
Brake fluid does not compress, but air does. If air gets into the lines - after a repair, a fluid change, or a leak - the pedal feels spongy because you are squeezing air bubbles instead of moving fluid. The fix is bleeding the brakes to purge the air.
Moisture in old fluid
Brake fluid absorbs water over time. Under hard braking, that moisture can boil into vapor, and vapor compresses just like air - giving a soft pedal exactly when you brake hard. This is why a fluid flush every 2 to 3 years matters. See our brake fluid guide.
A leak in the system
A pedal that slowly sinks to the floor under steady pressure can indicate a leak - at a caliper, a wheel cylinder, a hose, or the master cylinder - or a failing master cylinder seal. A visible fluid leak or a dropping reservoir level is a stop-driving-and-inspect situation.
Worn or misadjusted components
Badly worn pads, a sticking caliper, or a soft or bulging brake hose can all change pedal feel. Fresh pads, healthy brake hoses, and good hardware keep the pedal where it should be.
Do not ignore it
A spongy pedal means reduced, less predictable braking. Have the system inspected and bled - and if there is any sign of a leak, do not drive the vehicle until it is fixed. Brakes are not the place to wait and see.