Mercury vs Relay: Banking for a Civil or Structural Engineering Firm

A retention holdback, often a meaningful share of a project's total contract value, isn't cash you can plan around until it's actually released at project completion or an agreed milestone. Treat it as a memo item, not operating cash: track expected retention across all active projects in a running total, but never let it blend into your available balance in a way that makes current cash look healthier than it is. Relay's free sub-accounts can hold a placeholder balance for expected retention releases if you prefer tracking it inside the bank rather than in a separate spreadsheet, though either approach works as long as someone is actually maintaining it.

This discipline matters most when a firm is deciding whether it can afford to take on a new project, hire ahead of demand, or make a partner distribution. A firm that includes expected-but-unreleased retention in that decision is working from an inflated picture of what it can actually spend, and the gap between what looks available and what's truly liquid tends to surface at the worst possible time, right when a new project needs staffing and the cash everyone assumed was there turns out to still be tied up in a prior engagement's retention.

Keep retention from looking like cash with these steps:

1. Track expected retention across all active projects in a running total, kept apart from your available balance.
2. Treat it as a memo item, not operating cash, until it is actually released at completion or an agreed milestone.
3. Hold a placeholder balance in a Relay sub-account or a separate spreadsheet, whichever someone will actually maintain.
4. Leave expected retention out of decisions about taking on a project, hiring ahead of demand or making a partner distribution.

A firm running several multi-year projects at once needs to know, project by project, whether billed-to-date actually covers cost-to-date, not just whether the firm as a whole is cash flow positive this month. Mercury's account structure paired with its API lets a firm with a project accounting system pull balances and tag them against specific engagements; Relay's per-project sub-accounts accomplish something similar more simply, with a dedicated account per active project that makes a project running over budget visible well before the final invoice, when there's still time to have a change order conversation with the client instead of absorbing the overage.

Firms that collect a mobilization payment at project kickoff, common on larger civil projects, are holding a lump sum that needs to last through the early phases of the work before further billing catches up. The 10-year Treasury yield is at 4.44%¹, a useful reference for what conservative, liquid cash should be earning while it funds early-project costs. Mercury's automated Treasury sweep captures yield near current short-duration rates on cash above your operating buffer; a firm holding a mobilization payment for several months before it's fully drawn down is exactly the kind of situation that yield automation is built for.

Firms that front the cost of equipment rental, specialized surveys or subconsultant work before client reimbursement sometimes need a short-term credit line to bridge the gap. That credit is priced off the bank prime rate, currently 6.75%², so build that financing cost into how you price reimbursable pass-through items rather than treating it as a hidden cost the firm silently absorbs project after project.

A firm running dedicated project accounting or ERP software gets more from Mercury's API, since that system can pull real bank data directly rather than relying on someone manually reconciling bank statements against project ledgers. A smaller firm running project tracking in spreadsheets alongside QuickBooks or Xero is often well served by Relay's accounting integrations and its extra checking accounts on the free plan (up to 20 per business per its pricing page), at least until project volume grows enough to justify dedicated project accounting software and the API work that comes with it.rk that goes with it.

Larger engineering projects often involve subconsultants, a geotechnical firm, a specialty structural reviewer, a surveyor, billing the prime firm directly, with the prime then responsible for paying them regardless of when the client's own payment clears. Treat subconsultant liabilities the same way you treat your own payroll: reserve for them the moment you bill a milestone that includes their scope, not when their invoice actually arrives, since a subconsultant expecting prompt payment doesn't care whether your client has paid yet. Firms that let subconsultant payables float against general operating cash are the ones most likely to damage a specialty-firm relationship over a payment delay that a dedicated reserve would have prevented entirely.