How to reset the data every month?

I am getting user input, that collects in the data base.
There is one more row in the database, that stores the calculations of the inputs.
For ex. input A = 2, input B = 4
Input A X input B = C

Now I display the “C” on the screen according to day, week and month.
In month column, I display sum total of all “C” collected everyday.

For that I use:
SUM of C > created dated > after> 30 days ago

Now, I want to reset the displayed value of C to 0 on 1st of every month. But only on screen, and don’t want to alter the database to 0.