How do I implement a function in with Django Investment Website where a user gains dummy cash daily?

I'm testing my skills with Django Investment Website and I'm stuck now, I need to implement a function where a user can gain or watch thier dummy investment increase daily, e.g Invested $10 and their investment start growing from $10 - $20 - $40 etc daily. PLEASE ANY HELP FROM THIS GREAT COMMUNITY WOULD BE HIGHLY APPRECIATED