Mercury vs Relay: Banking for a Digital Marketing Agency

Relay's free sub-accounts are a natural fit here: open one dedicated account per major client's ad spend pass-through, fund it from that client's payment specifically, and pay the ad platforms out of that account rather than general operating cash. Your actual retainer or management fee revenue lands in a separate account entirely, so a glance at that balance tells you what the agency has actually earned, not what's sitting there waiting to be spent on someone else's campaigns. Mercury supports the same separation through its own multiple accounts, and for an agency running many client accounts, its API lets an ops-minded team pull balances into an internal dashboard next to campaign spend data rather than checking a banking portal client by client.

Separate pass-through ad spend from agency revenue in these steps:

1. Open one dedicated account for each major client's ad spend pass-through, so that money never blends with agency funds.
2. Fund each account from that client's payment specifically, rather than moving money in from general operating cash.
3. Pay the ad platforms out of that account, not out of operating cash, so the balance reflects client money only.
4. Keep retainer and management fee revenue in a separate account, so one glance shows what the agency has actually earned.

The real value of this separation shows up at contract renewal, when you need to show a client exactly how their ad budget was spent and confirm the agency never touched more of it than the management fee allows. An agency that's kept pass-through and revenue cleanly separated from the start can produce that accounting in minutes; one that hasn't is stuck reconstructing months of mixed transactions by hand, and that reconstruction is exactly the kind of work that erodes a client's trust if it takes too long or looks improvised.

Agencies billing retainers a month or a quarter in advance often carry a cushion of earned, unspent cash between when it's collected and when it funds payroll. Mercury's Treasury sweep automates capturing yield near the current effective federal funds rate, 3.63%¹, on cash above your working buffer, which applies cleanly to a retainer cushion that's genuinely the agency's own money, as opposed to client ad spend passing through. Keep that distinction firm: only sweep cash that belongs to the agency, never a client's ad budget sitting in a pass-through account waiting to be spent.

An agency bridging a gap between paying staff and collecting a late client invoice is borrowing at a cost tied to the bank prime rate, currently 6.75%². Before leaning on a credit line regularly, check whether specific clients are consistently the slow payers; an agency that's identified its two or three chronically late accounts can address that directly, through contract terms or a collections conversation, rather than financing around a pattern every month.

This is worth tracking formally rather than by memory. A simple monthly note of which clients paid late, and by how many days, turns a vague sense that "a couple of accounts are always slow" into a specific list you can act on: tightening payment terms at renewal, requiring a deposit before campaigns launch, or in persistent cases, deciding a client relationship costs more in financing than the retainer is worth.

Once ad spend pass-through and agency revenue are cleanly separated, the remaining choice between Mercury and Relay comes down to team composition more than anything else. An agency with an ops or data team already building internal dashboards gets real value from Mercury's API, pulling banking data in next to campaign performance data so account managers can see client profitability in one place. An agency running lean, without dedicated ops or engineering headcount, usually gets more immediate value from Relay: the sub-accounts are free and instant, and the native QuickBooks or Xero sync keeps a part-time bookkeeper's work current without any custom integration work. Neither choice locks you in permanently, and plenty of growing agencies start on Relay and add Mercury for a growing retainer reserve once the yield difference becomes worth the extra account.