Billing a Management Fee on Top of Client Ad Spend That Moves Every Month

The management fee is genuinely recurring: a percentage or a flat rate the client agreed to pay for the agency's work, independent of how much media they buy in a given month. The media spend passthrough is not recurring in the same sense; it's a reimbursement for a cost the agency fronted or coordinated, and its size depends entirely on the client's own budget decisions that month. Model these as two separate line items, even on one combined invoice, rather than one blended number. That split is what lets your own reporting show recurring agency revenue distinct from pass-through costs that carry no margin for you.

If the management fee is a percentage of spend rather than a flat number, Stripe's usage-based billing can calculate that percentage automatically once you report the month's spend as a metered event, which keeps the fee tied directly to what actually got spent rather than an estimate set at the start of the month. The tradeoff is the same one that shows up across usage-based setups: your team owns making sure the reported spend figure is accurate before the invoice generates, since Stripe has no independent way to verify it against your ad platform's own numbers.

Chargebee handles a percentage-of-spend fee through its usage-based pricing in a similar way, with the advantage that account managers can adjust a client's fee percentage directly in the platform if a contract renegotiation changes the rate, without an engineer touching the calculation logic. That flexibility costs more in licensing than Stripe Billing, so it tends to make sense once your agency is managing enough client accounts that account managers, not developers, need to be the ones making pricing changes.

Clients generally prefer knowing roughly what their invoice will look like before it arrives, and a fee that swings wildly with ad platform spend can read as unpredictable even when it's calculated correctly. Some agencies address this by billing the management fee on last month's actual spend rather than the current month's in-progress number, which trades a bit of real-time accuracy for a figure the client has already seen play out. Others bill against a committed monthly budget and true up the difference the following cycle. Neither platform makes this call for you; decide which tradeoff your client base prefers and configure the billing cycle to match, rather than defaulting to whichever timing is easiest to set up.

If a client pays their combined invoice by card, payment processing fees apply to the whole amount, including the media spend passthrough that carries no margin for the agency to absorb that cost against. Over a year, that's a real dent in an agency's own margin on an account with heavy ad spend. Structure the passthrough as an ACH or bank transfer item where possible, or build the processing fee explicitly into the client contract, rather than letting it quietly eat into the management fee's profitability without anyone noticing until a margin review.

Even a perfectly accurate variable invoice can read as confusing if the client has no context for why the number moved. Add a short summary line to each invoice, or a brief monthly note alongside it, showing the management fee, the total media spend it was calculated against, and the percentage rate, rather than expecting the client to reverse-engineer the math from a single combined total. That transparency costs almost nothing to set up in either platform's invoice template and heads off most of the billing questions that would otherwise land in an account manager's inbox every time spend shifts meaningfully from one month to the next. Most account managers can build this summary into an invoice memo field in either platform without any developer involvement, so there's little reason to skip it once the variable-fee structure is live.

Set up a variable-fee invoice this way:

• Model the management fee and the media spend passthrough as two separate line items, even when they appear on one combined invoice.
• Report each month's spend as a metered event so a percentage-based fee calculates from what was actually spent.
• Consider billing the fee on last month's actual spend when clients want an invoice amount they can predict in advance.
• Collect the passthrough by ACH or bank transfer where possible so card processing fees don't erode the agency's own margin.
• Add a summary line showing the fee, the media spend it was calculated against, and the percentage rate.