To invoice a customer for reimbursable expenses, list each expense as its own line item separate from your service fees, attach a receipt or log for every charge, and format the bill so it matches the categories and caps your contract already authorizes. Do those three things and most invoices clear on the first submission. Miss any of them and you’re waiting on emails from accounts payable instead of a deposit.
Check the Contract Before You Bill Anything
Your right to bill for out-of-pocket costs comes from the service agreement you signed. Whether it’s called a Master Service Agreement, a statement of work, or a signed engagement letter, the reimbursement clause is what gives you legal standing to charge beyond your base fee. That clause should list the categories the client will cover: travel, materials, subcontractor fees, shipping, technology costs, or whatever fits your work.
If the contract contains an integration clause (sometimes called a merger clause or entire agreement clause), the written document is treated as the complete deal between you and the client.1SEC. Master Service Agreement – Section: Article XXIX General Provisions Any expense category left out of the contract is fair game for the client to refuse, even if you both discussed it verbally. If you’re about to sign and the reimbursement clause is vague or missing a category you know you’ll need, fix it before signing. Adding a line item later is always harder.
Caps and Pre-Approval
Most well-drafted contracts impose caps on what you can spend. Airfare is typically limited to coach. Rental cars are often capped at mid-size. Hotel expenses are frequently benchmarked to the federal per diem lodging rate for that location, which in 2026 defaults to $110 per night for destinations without a specific higher rate.2U.S. General Services Administration. FY 2026 Per Diem Rates Book a $250-per-night hotel in a city where the contract caps you at the GSA rate and you eat the difference.
Some agreements require pre-approval for any single expense above a set dollar amount. A common threshold is $500, though it varies by client. Get approval in writing before you spend and attach the approval reference to the invoice. Submitting a large expense without the required approval code is one of the fastest ways to get an invoice kicked back.
Documentation That Survives Scrutiny
Every reimbursable charge needs proof. Clients want original receipts or clear digital copies showing the vendor name, purchase date, and amount paid. Any applicable sales tax should be visible on the receipt. For subcontractor costs, retain the third-party invoice showing exactly what was purchased and at what price. These documents create the audit trail your client needs to verify you aren’t padding expenses for profit.
Mileage Logs
If you’re billing for business travel by car, a mileage log is non-negotiable. The IRS requires you to record the date of each trip, your starting point and destination, the business purpose, and total miles driven.3Internal Revenue Service. Publication 463, Travel, Gift, and Car Expenses Most clients require the same level of detail. For 2026, the IRS standard mileage rate is 72.5 cents per mile, and many contracts use this rate as the default reimbursement figure.4Internal Revenue Service. 2026 Standard Mileage Rates Record mileage as you go. A log filled out from memory at month-end will have gaps, and those gaps give the client a reason to reduce your reimbursement.
Per Diem Instead of Receipts
Some contracts let you bill at the federal per diem rate instead of collecting individual meal and lodging receipts. For 2026 the standard meals and incidental expenses allowance is $68 per day, broken down into $16 for breakfast, $19 for lunch, $28 for dinner, and $5 for incidentals.2U.S. General Services Administration. FY 2026 Per Diem Rates The first and last day of a trip are reimbursed at 75% of that total, or $51. High-cost cities have significantly higher rates, so check the GSA tables for your destination. Per diem billing means you skip the coffee receipts, but you still document dates, locations, and business purpose for each trip.
How Long to Keep Records
Hold onto all receipts, logs, and supporting documents for at least three years after you file the tax return that includes those expenses. That’s the general IRS retention period for records supporting income and deductions.5Internal Revenue Service. How Long Should I Keep Records? Your client may have longer retention rules in the contract. Keep the originals regardless of what you submit with the invoice.
Building the Invoice
List each reimbursable expense as its own line item, separate from your service fees. Mixing reimbursable costs into a lump-sum service charge makes it impossible for the client’s accounts payable team to reconcile the bill, and it raises questions about whether you’re marking up expenses. Each line item should carry a brief description that mirrors the receipt, the date the expense was incurred, the amount, and any project or billing code the contract requires.
A clean invoice for a consulting engagement might look like this:
- Consulting services, Jan 1–31: $8,000.00
- Round-trip airfare, Chicago to Dallas, Jan 14: $342.00
- Hotel, Dallas, 2 nights at $129/night: $258.00
- Mileage, 86 miles at $0.725/mile: $62.35
- Printing and binding, project deliverables: $47.50
Attach all supporting receipts and the mileage log as subsequent pages in the same PDF or as linked files in a billing portal. The goal is to give the reviewer everything they need to approve the invoice without emailing you for documentation. Every follow-up email adds days to your payment timeline.
Keep the Reimbursement Off Your Taxable Income
How reimbursements are taxed depends entirely on how the arrangement is structured. This is where many service providers create unnecessary tax problems.
Accountable Plan Rules
An arrangement qualifies as an accountable plan when it meets three requirements: the expenses must have a business connection to the work performed, you must substantiate each expense with documentation within a reasonable time, and you must return any reimbursement that exceeds the documented costs.6Internal Revenue Service. Publication 15 (2026), Circular E, Employer’s Tax Guide When all three are met, the reimbursement is not treated as income. For independent contractors, properly accounted-for reimbursements are excluded from the 1099-NEC the client files.7Internal Revenue Service. Instructions for Forms 1099-MISC and 1099-NEC
Your invoice documentation does double duty here. The same receipts and logs that satisfy the client also satisfy the IRS substantiation requirement. Skip the documentation and the arrangement fails the accountable plan test.
What Happens Without an Accountable Plan
When the arrangement doesn’t meet all three requirements, the IRS treats the entire payment as compensation.8eCFR. 26 CFR 1.62-2 – Reimbursements and Other Expense Allowance Arrangements For an independent contractor, the reimbursement gets lumped into the 1099-NEC total, increasing your reported income.7Internal Revenue Service. Instructions for Forms 1099-MISC and 1099-NEC You can still deduct the underlying business expenses on Schedule C, but you’re now paying self-employment tax on money that was supposed to be a pass-through cost. That’s an avoidable 15.3% hit on every dollar of improperly structured reimbursement.
Markup Is Revenue
If you add a handling fee or percentage markup to reimbursable expenses, the marked-up portion is your revenue, not a reimbursement. Some providers bill materials at cost plus 15% or charge a flat administrative fee on top of travel costs. That’s a legitimate practice, but the markup is taxable income, and it may also trigger sales tax obligations depending on your jurisdiction. Keep the markup as a separate line item so there’s no confusion about which portion is a pass-through cost and which is your fee.
Sales Tax on Reimbursed Expenses
Whether you need to charge the client sales tax on reimbursable expenses depends on your state’s rules and the nature of the service. In many jurisdictions, when you pay for materials or services as part of delivering a taxable service, the reimbursed amount is considered part of your gross receipts and carries the same tax treatment as the service itself. Taxable service, taxable reimbursements. Exempt service, exempt reimbursements. Confirm the rules with a tax professional or your state’s revenue department, especially if you work across state lines.
Getting Paid on Time
Most clients accept invoices through an accounting portal or by email. For portal submissions, upload the invoice and all supporting documentation together. For email submissions, attach everything in a single PDF. Sending the invoice as one file with receipts appended behind the main billing page reduces the chance that a receipt gets separated and triggers a document request.
Payment timelines are usually defined in the contract as “Net 30” or “Net 60,” meaning the client has 30 or 60 days from receiving a proper invoice to issue payment. If your contract doesn’t specify payment terms, you’re at the mercy of the client’s standard processing cycle. Spell out the terms you want before you sign.
If a client disputes a specific line item, respond quickly with the supporting receipt or additional context. A disputed item doesn’t need to delay the entire invoice. Ask whether the client can process the undisputed portion while the questioned charge is resolved. Most accounting departments can split payments when asked. Payments typically arrive via ACH transfer or corporate check, with ACH being the faster option by several days.
Following Up and Late Interest
Check in on the status of your invoice about two weeks after submission if you haven’t received confirmation that it’s queued for payment. A polite follow-up at that point catches processing delays before they snowball. If the payment deadline passes, your contract’s late-payment clause kicks in. Many agreements include a monthly interest charge on overdue balances, and the permissible rate varies widely by state. Federal contracts follow the Prompt Payment Act, which sets the interest rate at 4.125% annually for the first half of 2026.9U.S. Department of the Treasury. Prompt Payment Private contracts aren’t bound by that rate, so whatever your agreement specifies will control. If your contract is silent on late fees, you have little leverage to charge interest after the fact.
Foreign Currency Expenses
When your work involves expenses paid in a foreign currency, convert those costs to U.S. dollars on the invoice. The standard approach uses the exchange rate from the date the expense was incurred. Your bank or credit card statement will usually show the converted amount and the rate applied, which serves as your documentation. If the contract specifies a different conversion method, follow the contract. Include both the original foreign currency amount and the converted U.S. dollar figure on each line item so the client can verify the math. Rounding discrepancies on currency conversions are a surprisingly common source of invoice disputes, so show your work.