We use the equal principal and interest repayment method to calculate the monthly repayment amount, which is a common calculation method.

The monthly payment formula of M is: M equals P multiplied by "r/( 1 minus (1 plus R) (minus N)", where R is the monthly interest rate (annual interest rate/12) and N is the total number of months (years multiplied by 12).

As can be seen from the title conditions, P is equal to 2,500,000, the annual interest rate is unknown, and the loan term is 20 years. If the formula is substituted, the calculation result is: 16498.89 yuan, then we need to pay back 16498.89 yuan every month.