How to tell the difference between air being in the brake lines or needing to replace the master cylinder?

I have to push further down to stop my car. It's not that bad but I'm taking the car in Monday. I d rather be safe then sorry. When the car is stopped I pump the brakes and it stiffens but then if I push hard the pedal still goes down. It kinda feels like the pedal doesn't stiffen until 2/5 of the way down. There's still plenty of break fluid so it doesn't look like a leak… Model: 2004 Ford Escape.

That's the symptoms of a bad master cylinder.

If you step on the brakes and hold and then the pedal goes down further then you need a new master cylinder.