Tracking Billable Expenses You Pass Through to Clients

Every consultant, agency and contractor eventually fronts money for a client: a flight, a stock photo license, a permit fee, lunch with their vendor. The work is easy. Remembering which of those costs belongs on which invoice, sixty days later, is where the money quietly leaks out.

What actually counts as a billable expense

A billable expense is a cost you incur on a client's behalf and expect to recover, either at cost or with a markup. The test is not "was this work related," it is "did my agreement with this client say I can rebill it." Common examples: travel and mileage for on-site work, subcontractor invoices, software or asset licenses bought for a specific deliverable, shipping, printing, permit and filing fees, and equipment rental.

What is usually not billable: your own tools and subscriptions, general office costs, your commute, and anything the client never agreed to in writing. Those are overhead. They are still deductible business expenses, but they belong in your own books, not on the invoice. Sorting a cost into the right bucket at the moment you pay is the single highest leverage habit here, because that classification is nearly impossible to reconstruct from a bank statement line that just says a merchant name and a number.

Reimbursement or markup: pick one and write it down

There are two clean ways to handle pass-through costs, and trouble comes from mixing them silently.

• At cost (reimbursement). You rebill the exact amount you paid. Clients like it, it is easy to defend, and it invites receipt-level scrutiny, so your documentation needs to be tight.
• Cost plus markup. You add a percentage to cover the admin burden and the cash you fronted. Perfectly normal, but the markup must be in the contract. Discovering it on an invoice makes clients feel handled.

Whichever you choose, put three things in the engagement letter: which categories are rebillable, whether a markup applies and at what rate, and any per-item or monthly cap above which you need written approval. That last one prevents the most common dispute in this whole area, which is a client refusing a cost they would have approved if asked first.

The receipts you need to keep, and for how long

Pass-through expenses carry a double record-keeping burden. You need the receipt for your own tax records, and you need a legible copy to substantiate the charge to your client. A receipt that supports a rebill should clearly show the merchant, the date, the total, any sales tax, and enough line item detail that the client can see what they are paying for. A blurry photo of a folded taxi slip satisfies nobody.

On retention: keep supporting records for the longest window that could apply to you. In the US that generally means at least 3 years from filing for routine situations and longer in specific cases, and in Canada the CRA generally expects 6 years. Digital copies are accepted by both as long as they are accurate, complete and readable, so there is no reason to keep the paper once you have a clean scan.

One extra detail that matters for rebilled costs: note who the expense was for and why, on the record itself. "Client name, project, purpose" takes four seconds at capture and saves a twenty minute archaeology session at invoicing time.

A monthly workflow that takes ten minutes

The workflow that survives a busy month is the one with no batch step at the end. Try this:

1. Capture at the counter. Photograph the receipt before you pocket it. Scanning pulls the merchant, date, total, tax and line items off the image, so there is nothing to type.
2. Tag it immediately. Confirm the category and add the client or project name while you still remember the context.
3. Flag rebillable versus overhead. A single consistent marker is enough. Consistency beats cleverness.
4. Reconcile weekly, not monthly. Five minutes on a Friday to catch missing receipts is far cheaper than an hour at month end guessing at a card statement.
5. Export at invoicing. Pull a CSV of the period, filter to the client, and attach the receipts to the invoice. Clients who can see the backup approve faster and query less.

The three mistakes that cost real money

Unbilled costs. Expenses you paid, never tagged, and never invoiced. This is pure lost margin and it is invisible, which is why it persists for years.

Double-counting income. If you rebill a cost and also claim the original as a deduction without recording the reimbursement as income, your books will be wrong. Treat the rebill and the underlying cost as a matched pair.

Surprise line items. Costs the client never approved. Cap it in the contract, ask before you exceed the cap, and attach the receipt. Every dispute you avoid is time you get to bill instead.

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