What is the formula to calculate the mortgage payments for a house?

What is the formula to calculate the mortgage payments for a house?
Added (1). So lets say, the house is $400,000
The payment term is 30 years.
there is some interest rate.
I am ready to pay 5% initial payment.
what will the approximate monthly payment for the house? If its FHA loan
Added (2). What if my credit is excellent? Will that bring the payments down?

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