How to Invoice the Federal Government (IPP, WAWF, 2026)

Quick answer: To invoice the federal government, register your business in SAM.gov to get a Unique Entity ID and set up electronic payment, then submit a proper invoice through the system named in your contract, usually Treasury's Invoice Processing Platform (IPP) for civilian agencies or PIEE/WAWF for the Department of Defense. Payment is generally due 30 days after a proper invoice is received.

Winning a government contract is the hard part. Getting paid should be routine, but first-time contractors often lose weeks to rejected invoices, expired registrations or the wrong portal. This guide explains how to invoice the federal government in 2026: registration, which invoicing system to use, what makes a proper invoice under the Federal Acquisition Regulation (FAR), how Prompt Payment Act interest works, a worked example and the mistakes that delay payment. This is general information, not legal advice; your contract's terms control.

What do you need before invoicing the federal government?

Requirement	What it is	Where to get it
SAM.gov registration	Entity registration required for most prime contracts; renew every year	SAM.gov (free)
Unique Entity ID (UEI)	12-character ID that identifies your business on contracts and payments	Assigned in SAM.gov
CAGE code	Commercial and Government Entity code, assigned during SAM registration for US entities	Assigned during registration
EIN or TIN	Taxpayer identification number, validated with the IRS	IRS; see how to get an EIN
Banking details	Account for electronic funds transfer (EFT) payments	Entered in your SAM registration
Invoicing system account	IPP, PIEE/WAWF or the agency's own system	Per your contract instructions

Registration is free. Start early, because SAM registrations can take time to activate, especially if your business details need validation. Make sure your legal business name and address in SAM match your IRS records exactly, because mismatches are a frequent cause of delays.

Which system do you use to submit invoices?

The government does not have one single invoicing portal. Your contract, order or agreement tells you where to submit, usually in a clause on electronic invoicing or in the "invoice instructions" section. The main systems are:

Invoice Processing Platform (IPP)

The Invoice Processing Platform is run by the Treasury Department's Bureau of the Fiscal Service. Many civilian agencies use it to send purchase orders to vendors, receive invoices and send payment notifications. Treasury describes IPP as free for agencies and vendors. Agencies that adopt IPP typically send each vendor an enrollment email with login instructions; you then submit invoices against the purchase orders shown in your account and can track their status.

PIEE and Wide Area Workflow (WAWF)

The Department of Defense uses the Procurement Integrated Enterprise Environment (PIEE) at piee.eb.mil. Inside PIEE, the Wide Area Workflow (WAWF) application handles invoices and receiving reports. DoD contracts generally include DFARS clause 252.232-7006, which requires electronic submission through WAWF and lists the document type and routing codes to use. You register in PIEE, request the Vendor role for your CAGE code, and your company's electronic business point of contact approves it.

Agency-specific systems and email

A few agencies use their own portals, and some small orders still allow email submission to a designated billing office. If the contract names a system, use it; invoices sent anywhere else may never reach the paying office.

Is there a 2026 consolidation of federal invoicing systems?

More agencies continue to move onto IPP, and some have announced migrations in 2026 (for example, NIST notified vendors of a move to IPP with a temporary pause in invoice submissions). As of October 2026 we found no single governmentwide deadline replacing all agency systems with one portal, and DoD still uses PIEE/WAWF. Separately, the FAR itself has been undergoing a major rewrite since 2025, so clause numbers and wording in new contracts may differ from older ones. Always follow the invoice instructions in your own contract and any notice from your contracting officer.

What is a proper invoice?

The Prompt Payment clock only starts when the billing office receives a proper invoice. FAR 32.905 lists what a proper invoice must contain:

• Your business name and address, matching your SAM registration.
• Invoice date and a unique invoice number. A clear invoice numbering system helps.
• Contract number or other authorization, including the order number and contract line item number (CLIN).
• Description, quantity, unit of measure, unit price and extended price of the goods delivered or services performed.
• Shipping and payment terms, such as shipment number and date of shipment, if applicable.
• Name and address of the contractor official to whom payment is to be sent, if different.
• Name, title and phone number of the person to notify about a defective invoice.
• Your taxpayer identification number (TIN), unless already in your registration as the contract allows. See tax ID on an invoice for how to show it.
• Electronic funds transfer banking information, if required by the contract.
• Any other information or documentation the contract requires, such as timesheets or receiving reports.

The government matches your invoice to the contract and to evidence that the goods or services were received and accepted, similar to a commercial three-way match. Anything that does not match, such as a quantity above what was ordered, will cause a rejection.

How to invoice the federal government step by step

1. Register in SAM.gov and confirm your UEI, CAGE code and banking details are active.
2. Read the contract's invoicing instructions. Note the system, billing frequency, required documents, CLINs and the designated billing office.
3. Set up your system account. Respond to the IPP enrollment email, or register in PIEE and request the Vendor role.
4. Deliver and document. Keep delivery receipts, timesheets or acceptance records the contract asks for.
5. Prepare the invoice. Bill only what was delivered or performed in the billing period, by CLIN, at contract prices.
6. Submit through the required system. In WAWF, choose the document type the contract specifies (for example, a combined invoice and receiving report for many supply contracts).
7. Track status. IPP and WAWF show when an invoice is received, approved, rejected or paid.
8. Fix rejections quickly. A corrected proper invoice restarts the payment clock.
9. Reconcile payments. Match deposits and remittance details to each invoice, and check any Prompt Payment interest.

When will you be paid, and what if it is late?

Under the Prompt Payment Act, payment on most contracts is due 30 days after the designated billing office receives a proper invoice, or 30 days after government acceptance, whichever is later. Agencies should return an improper invoice with reasons, generally within seven days. The FAR also directs agencies to accelerate payments to small business contractors where possible, with a goal of paying within 15 days of a proper invoice.

If the government pays late, interest is generally added automatically, without you having to ask. Treasury publishes the rate every six months on its Prompt Payment interest rate page; for July 1 to December 31, 2026 it is 4.75% a year. Interest is calculated on a 360-day year.

Worked example: a federal services invoice

BrightPath Training LLC has a firm-fixed-price contract with a civilian agency for staff training, with invoices submitted monthly through IPP. In October 2026 it delivered four on-site sessions and the course materials.

CLIN	Description	Qty	Unit	Unit price	Amount
0001	On-site leadership training session, 1 day	4	Each	$6,250.00	$25,000.00
0002	Participant course materials	80	Each	$45.00	$3,600.00
0003	Post-training assessment report	1	Each	$2,400.00	$2,400.00
Total amount due					$31,000.00

The invoice shows the contract and order number, invoice number BPT-2026-010, invoice date November 2, 2026, service period October 1 to 31, 2026, the UEI, the contact for invoice problems and a note that payment is by EFT to the account in SAM.

The billing office receives the proper invoice on November 2. Acceptance happened on October 31, so the due date is 30 days after receipt: December 2, 2026. Suppose payment arrives on December 22, 20 days late. Interest at 4.75% would be about $31,000 x 4.75% x 20 / 360 = $81.81, added to the payment. If the invoice had been rejected for a wrong CLIN and resubmitted on November 12, the clock would restart and the due date would move to December 12.

Common mistakes when invoicing the government

• Letting SAM registration expire. Payments can stop until it is renewed. Set a reminder well before the renewal date.
• Using the wrong system or document type. Check the contract clause every time, especially with a new agency.
• Billing ahead of delivery. Unless the contract allows advance or progress payments, bill only for accepted work. For long projects, contracts may provide for partial or progress billing.
• Mismatched details. Name, address and bank details must match SAM; CLINs, prices and quantities must match the contract.
• Missing documents. Timesheets, receiving reports or certifications required by the contract.
• Duplicate submissions. Resubmitting the same invoice number in a different system creates confusion and delays.
• Ignoring rejection notices. Check the system regularly; each day an invoice sits rejected is a day of unpaid work.
• Paying for "free" services. SAM registration, IPP and PIEE cost nothing to use.

What about purchase cards and small orders?

Not every federal sale goes through IPP or WAWF. For small purchases, agencies often pay with the Government Purchase Card, a Visa or Mastercard issued to authorized federal buyers. In that case you take a normal card payment and provide a receipt or invoice for the buyer's records; there is no portal submission and no Prompt Payment clock. Your invoice should still show the buyer's name, agency, order details and a clear description, because cardholders must keep documentation for their purchases. Ask the buyer before adding any card surcharge or fee, since card rules and agency policy apply.

How invoicing works for different contract types

Contract type	What you bill	Typical supporting documents
Firm-fixed-price supplies	Quantities delivered and accepted, at contract unit prices	Receiving report or combined invoice and receiving report, shipping documents
Firm-fixed-price services	Monthly or milestone amounts set in the contract	Evidence of performance, deliverables accepted
Time-and-materials or labor-hour	Hours by labor category at contract rates, plus allowable materials	Timesheets, labor category mapping, material receipts
Cost-reimbursement	Allowable incurred costs plus fee	Cost vouchers; often subject to audit by the contracting agency
Construction	Progress payments based on work completed, less retainage if applicable	Schedule of values, progress estimates, certifications

The more complex the contract type, the more documentation the government needs before it can pay, and the more important it is to set up your billing process before the first invoice is due. If your company is new to retainage on construction contracts, our guide to retainage invoices explains how withheld amounts are shown and released.

Tips for small businesses new to federal invoicing

• Keep a contract summary sheet: contract number, CLINs, prices, billing office, system and contracting officer contact.
• Use the system's training. Treasury and DoD offer vendor training and help desks for IPP and PIEE.
• Prepare your own PDF too. Even when you key data into a portal, drafting the invoice first in our free invoice generator gives you a clean record and a checklist of every line.
• Accept ACH only. Federal payments arrive by EFT; see how to accept ACH payments to understand timing and remittance data.
• Watch cash flow. Even on-time payment can mean 30 to 45 days from delivery. Plan for it as you would with any net 30 customer.

Paper checks are also on the way out: a March 2025 executive order directed Treasury to stop issuing paper checks for most federal payments from September 30, 2025, with limited exceptions, so accurate bank details in SAM matter more than ever.

Invoicing the federal government is mostly about precision: the right registration, the right system and an invoice that matches the contract line by line. Draft and keep a copy of every invoice with our free invoice generator: it is free, needs no sign-up and creates a PDF in your browser that you can keep alongside your IPP or WAWF submissions.