Calculations that SLOW db down. Fix How?

Hello,

I am developing a system that tracks payments and balances due or owed on a monthly basis. I'm using relationships/calculations that look back to previous months to bring balances due or owed into the most recent month. The problem is, the db slows down during data entry on these pages. If the user does data entry that will change the balance, the db takes some time to refigure the balance. I want the user to be able to fly through data entry and to not have to pause while the db recalculates. I can't figure out if this is a common problem and I need to figure out a work around using scripts to set the balances in number fields to speed things up - OR if I am going about the way I have set the calculations and relationships incorrectly. Please advise or show me examples of a similar system. I hope I have explained my problem clearly enough! THANKS