Deposit and draw schedule
The deposit has one job: make sure you are not funding the customer's materials out of your own account. This splits the total and tells you whether it does.
Result
Check the deposit against your material cost for the job. If materials exceed the deposit, you are lending the customer money at 0% and carrying the risk.
Questions
What is a normal deposit for a painting job?
Commonly 25–35%, and some jurisdictions cap what you may take before work starts — check your local rules.
Can customers pay a deposit by card?
In Aerys, yes — the estimate carries the accept link, and accepting it opens the payment page on the same link.
Or stop doing this in a calculator
Aerys prices the whole job from your own catalog and production rates, sends it with an accept link and an invoice already attached, and then tracks what the job actually cost against what you quoted.