Whether to send an invoice before or after payment depends on how your business gets paid. If you deliver goods or services on credit — the standard in most business-to-business work — you invoice first and the buyer pays within the terms you agreed to. If the customer pays at the point of sale, as in retail and e-commerce, the invoice comes afterward and functions as a receipt. A few situations sit between those two, and your accounting method changes what the timing means for your taxes.
When to Invoice Before Payment
Invoicing before payment is the default in B2B transactions. You complete the work or ship the goods, send the invoice, and the buyer pays within the credit window you negotiated. Terms like “Net 30” or “Net 60” give the buyer 30 or 60 days from the invoice date to remit the full balance.
If your agreement says nothing about payment terms, the Uniform Commercial Code fills the gap: payment is due when the buyer receives the goods.1Cornell Law School. UCC 2-310 – Open Time for Payment or Running of Credit; Authority to Ship Under Reservation Without written terms, you don’t have to wait 30 days — the buyer technically owes you at delivery. Most sellers still spell out payment terms directly on the invoice to avoid ambiguity.
Federal government contracts have their own rule. Under the Prompt Payment Act, agencies must pay within 30 days of receiving a proper invoice, or another period the contract specifies, and interest accrues automatically if they miss the deadline.2eCFR. 5 CFR Part 1315 – Prompt Payment Vendors don’t have to ask for the interest; the agency owes it on its own.3Acquisition.GOV. FAR Subpart 32.9 – Prompt Payment The Prompt Payment Act covers federal agencies only. If a private client pays late, your remedies come from the contract and your state’s law.
When to Invoice After Payment
When the customer pays first, the invoice comes after the money changes hands. Retail sales, e-commerce checkout, and card-on-file charges all follow this pattern. The document is proof of purchase rather than a request for funds, and point-of-sale systems and payment gateways generate it automatically once the charge clears.
Prepaid retainers and deposits work the same way. When a client sends a retainer before work begins, you issue a post-payment invoice recording the amount received and what it covers. Later invoices then draw down from the balance as you do the work. The client gets a clear record of what they paid, and you have documentation tying each payment to specific services.
Post-payment invoices matter on the buyer’s side too. Businesses claiming purchases as deductions rely on invoices to substantiate those expenses, and a legitimate expense without a proper invoice can be challenged during an audit.
Milestone Billing for Long Projects
Large projects rarely fit neatly into either category. Instead, you invoice multiple times, with each invoice tied to a defined milestone: completing the foundation, delivering a prototype, finishing a phase. The master contract spells out which milestones trigger an invoice and how much each one is worth.
The approach keeps cash flowing to the provider while giving the client checkpoints before releasing more money. Most milestone agreements include a clause pausing further work if a milestone invoice goes unpaid past its grace period.
Pro Forma Invoices Are Not the Same Thing
A pro forma invoice looks like an invoice but functions as an estimate. It shows what the buyer would owe if they proceed, without creating a payment obligation. The U.S. International Trade Administration describes it as “a quote in an invoice format” that buyers often need to apply for import licenses, open letters of credit, or arrange currency transfers.4Trade.gov. Pro Forma Invoice
A pro forma is not legally binding and cannot be used for tax reporting or customs clearance. Once both parties agree to proceed, you replace it with a standard commercial invoice that carries legal weight. Treating a pro forma as a final invoice, or skipping the commercial one, creates problems at customs and in your books.
How Invoice Timing Affects Your Taxes
When you send an invoice can shift when the income hits your tax return, and the answer depends on whether you use cash-basis or accrual-basis accounting.
Cash Basis
Under the cash method, you report income in the year you actually receive payment.5Internal Revenue Service. Accounting Periods and Methods A December invoice for work you completed doesn’t create taxable income that year if the check arrives in January. The invoice is a request; the tax event happens when money lands in your account or becomes available to you without restriction.
That “available without restriction” language matters. It’s called constructive receipt: if a client’s check is sitting in your mailbox on December 31, the IRS considers that income received in December even if you don’t deposit it until January.6eCFR. 26 CFR 1.451-2 – Constructive Receipt of Income You can’t defer income by ignoring payments that are available to you.
Accrual Basis
Accrual-method taxpayers report income when they earn it, regardless of when payment arrives. The IRS uses the all-events test: income is recognized when you’ve performed the work, when payment becomes due, or when you receive payment, whichever happens first.5Internal Revenue Service. Accounting Periods and Methods For most service businesses, completing the work is the trigger. An accrual-basis consultant who finishes a project in November but doesn’t invoice until January still owes tax on that income for November’s tax year.
If a client pays in advance, accrual-method businesses generally must report that advance payment as income in the year received. You can elect to defer it to the following year, but no further than that.5Internal Revenue Service. Accounting Periods and Methods
What Every Invoice Should Contain
No single federal statute dictates the exact contents of a domestic commercial invoice, but federal law does require every taxpayer to keep records sufficient to establish gross income and deductions.7Office of the Law Revision Counsel. 26 U.S. Code 6001 – Notice or Regulations Requiring Records, Statements, and Special Returns Your invoices need to work as source documents for your books, regardless of when you send them.
Every invoice should show:
- Your business’s legal name, address, email, and phone number.
- The buyer’s name, company if applicable, and billing address.
- A unique, sequential invoice number for tracking.
- The date of issue, which starts the clock on payment terms.
- Line-item descriptions with quantities, unit prices, and subtotals.
- The total due, with any sales tax stated as a separate line item.
- Payment terms and accepted methods.
Separately stating sales tax isn’t just tidy. Under the Streamlined Sales and Use Tax Agreement, certain charges like shipping fees can only be excluded from the taxable sales price if they appear as separate line items. Lumping everything into one number can increase the tax owed.
If sloppy recordkeeping leads you to underreport income, the accuracy-related penalty under federal law is 20% of the underpayment.8Office of the Law Revision Counsel. 26 U.S. Code 6662 – Imposition of Accuracy-Related Penalty on Underpayments That’s a percentage of the tax you got wrong, not a flat fine, and it can add up quickly.