This project invoice calculator splits a fixed project fee into a deposit and equal installments. It adds tax first, then builds a payment schedule. You see the project total, the deposit, each installment and the running total after every payment.
The formula
tax = project fee x tax rate
total = project fee + tax
deposit = total x deposit % (rounded to cents)
remaining = total - deposit
installment = remaining / installments (rounded to cents)
The last installment equals the total minus all earlier payments. The number of installments is capped at 60.
Worked example
Inputs: project fee $5,000, tax 10%, deposit 30%, 3 installments.
- Tax: $500.00
- Project total: $5,500.00
- Deposit: $1,650.00
- Remaining: $3,850.00
- Installments: $1,283.33, $1,283.33 and $1,283.34
The schedule has four payments. The running total ends at $5,500.00.
How to read the result
The schedule shows each payment as a share of the total. Use it as a payment plan inside a contract or quote.
- A larger deposit lowers your risk and helps cash flow.
- Tie each installment to a milestone or a date, not only to a count.
- Send the deposit invoice first. Send each later invoice when its milestone is done.
- Equal installments suit retainers and long builds. Milestone work often needs unequal steps.
Tax rules differ by country. Check how your region treats deposits with a tax authority or an accountant.
Related tools
- Create the document: Invoice generator and Proforma invoice generator
- Read more: Invoice deposits and Payment plans
- Other calculators: Contractor invoice calculator and Invoice calculator
Frequently asked questions
- How do I split a project fee into payments?
- Add tax to the fee to get the project total. Take the deposit as a percent of that total. Divide the remaining amount by the number of installments. The last payment absorbs any rounding.
- How big should a project deposit be?
- There is no fixed rule. The right figure depends on your upfront costs, the client and the project size. Agree it in writing before you start. The default here is 30 percent.
- Is the deposit calculated before or after tax?
- After tax. This calculator applies the deposit percentage to the project total that already includes tax, so every payment includes its share of tax.
- Why is the last installment different?
- Dividing the balance can leave fractions of a cent. The last installment takes the difference, so the schedule adds up exactly to the project total.
- Can I use zero installments?
- Yes. With zero installments, the schedule has only the deposit. Set the deposit to 100 percent if the client pays the full amount at once.