Claude vs ChatGPT: Time Tracking Multiple Clients Separate Billing. Join the debate.

For this, I'd go with FreshBooks — it's built around exactly this workflow, with per-client billing, time tracking, and reporting that keeps each client completely separate without you having to build workarounds.

FreshBooks handles both cleanly in the same account — you can log billable hours against hourly clients and set flat-rate invoices for retainer clients, and the reporting separates them by client rather than forcing a single billing model. The friction point is when one client has mixed billing — say, a retainer plus occasional hourly overages — because FreshBooks doesn't natively flag "retainer hours used vs. overage hours" in one view. You'd manage that manually or with a note system. If mixed-model billing is common across your client base, Harvest handles that boundary more elegantly with its budget-vs-time tracking per project.

Yes — FreshBooks invoices both hourly and retainer clients from one system, no external tools needed. But given that you're managing multiple clients with mixed billing types, my final recommendation is Harvest over FreshBooks. Harvest's per-project budget tracking means you can set a retainer cap, log hours against it, and see exactly when a client crosses into overage — all before you invoice. FreshBooks is cleaner to use day-to-day, but Harvest was built for precisely this complexity: multiple clients, mixed billing models, and reporting that keeps each engagement legible without manual reconciliation. Start on the free trial — it covers two projects and will show you immediately whether the workflow fits.