how to create balance amount?

Question

i have successfully create the receipt form of my loan payment application.

but i need to create the late pay interest,and delayed payment are show in textbox..............

please help me.......................... 

 

say exaple:loan start date is:02/02/2018 

                           End date is:(02/02/2018)+100days=date

                          the customer cannot pay the amount daily,then how to show up to date payable amount and late pay interest..................