can u improve this sentence?

For a loan, you have to repay the principal and the interests upon it's due day.
The word "principal" can replace the phrase "the money that you have borrowed".
For a loan, there should be a due day for repayment, therefore interests shall be incurred. As such, I add the criteria of "upon it's due day"

A loan is the sum of money you borrow from someone. You have to repay the money plus monthly interest.
Interet is an uncountable noun here.

For the money you have borrowed, you have to repay both the principal and the monthly interests.

principal 本金

After you borrowed a loan, you have to repay the money with the interests that you have borrowed.

Just my opinion!

the sentence is just fine