Home Loans – How Do You Estimate How Much Your Monthly Pmt Would Be?

For example, if your house was $375,000 – how do you estimate what your monthly payment would be? Or for any amount??

Is It Fianancially Sound to Move 50K from 401K to Reduce Mortagage and Refinance at a Lower Payment?

I am 63 and want to retire in the next year. Reducing my mortgage pmt by half would make retirement simpler. I have 180k in my 401k.