The Fixed-Fee Fallacy: WIP Still Tells You the Truth
Moving to fixed fees doesn't mean you can stop tracking time. WIP is how you find out whether your prices actually work — before the year is gone.
There's a comfortable myth doing the rounds in practice-owner circles: once you move to fixed fees, you can throw out the timesheets. No more billing by the hour, no more WIP ledgers, no more nagging staff to log their day. The fee is the fee, the client pays it, everyone's happy.
It's a seductive idea. It's also how firms quietly bleed margin for a full financial year without noticing.
Fixed fee changes the invoice, not the economics
Fixed pricing changes how you charge. It doesn't change the fact that every job consumes real hours, and those hours have a cost. When you bill by the hour, the meter and the price move together — if a job blows out, the invoice grows with it. Painful for the client, but at least visible to you.
Fixed fee severs that link. The price is locked in at engagement, but the effort is still variable. Which means the only way to know whether a job made money is to compare the fee you agreed against the time it actually took. No time data, no comparison. You're flying on vibes.
This is the trap. Firms drop time tracking because "we don't bill by the hour anymore" — and in doing so they delete the exact measurement that tells them whether their fixed fees are set correctly.
WIP under fixed fee: still the truth-teller
Work-in-progress is usually described as unbilled time waiting to be invoiced. Under fixed fee, its role shifts but doesn't disappear. Here WIP becomes your running tally of effort committed against a fee already agreed.
Say you quoted a company tax return and accounts prep at $3,300. As your team works the job, time accrues against it. If you're logging that time, you can watch WIP climb: $1,200, $2,400, $3,600. The moment WIP passes the fee, you're working at a loss on that engagement — and you'd never know if the timesheet was empty.
Multiply that across a hundred fixed-fee jobs and the picture matters. Some will come in under. Some over. The average is your real recovery rate, and the outliers tell you which client types, which job templates, and which staff need attention. That's not hourly-billing nostalgia. That's the basic feedback loop any pricing model needs to survive.
The jobs that quietly eat the year
The dangerous fixed-fee jobs aren't the obvious blowouts. They're the ones that run 20% over, every time, on a client you've had for years. Nobody flags it because there's no invoice surprise — the client pays the same $3,300 they always do. Without WIP against fee, that 20% is invisible. It just shows up as a practice that feels busy and profits less than it should.
Good accounting practice management software surfaces these before they compound. In Finye, time logged against a job sits next to the agreed fee on that job, so you can see budget-versus-actual on every engagement without building a spreadsheet. The over-runs stop being a year-end shock and start being a weekly signal.
What to actually track (even when you don't bill by it)
You don't need six-minute-increment granularity to make fixed-fee WIP work. You need enough to answer three questions:
- Which job did this time go to? Time logged against a client but not a job is nearly useless for pricing. Every hour should attach to a specific engagement.
- How does effort compare to the fee? The single most valuable number is committed hours (at cost) versus the agreed price for that job.
- Where in the workflow is the time going? A return that runs over because of endless PBC chasing is a different problem from one that runs over in review. The fix is different too.
That last point matters. A lot of fixed-fee over-run isn't the technical work — it's the coordination around it. Chasing documents, re-requesting the same bank statement, waiting on a signature before anyone starts. If your client accounting workflow leaks time in the gaps between steps, no pricing model saves you. You fix it by tightening the workflow, and you only know to do that because the time data pointed there.
WIP ageing still applies
Even under fixed fee, timing matters. If you deliver a job in July but don't raise the invoice until October, you've carried that WIP for a quarter and taught the client that delivery and payment are unrelated. A WIP ageing view — showing how long completed work has sat unbilled — keeps the gap between finishing and invoicing short.
The cleanest version of this is billing tied to a milestone rather than a mood. When the engagement is signed, or the job hits "ready to invoice," the bill goes out. Finye lets you trigger invoicing from job status and syncs the invoice through to Xero, so the WIP doesn't quietly age while everyone's heads-down on the next deadline. The point of good accounting client management software isn't to replace your judgement on price — it's to make sure the money you already agreed to actually gets billed, on time, every time.
Fixed fee is a bet — WIP tells you if you won
Every fixed price is a wager: you're betting the job takes roughly the hours you assumed. Some bets pay off, some don't. A firm that tracks time is running the numbers on those bets and adjusting next year's prices with evidence. A firm that dropped timesheets when it "went fixed fee" is placing the same bets blind, year after year, and calling the losses a busy season.
You don't keep time to bill by it. You keep it to know whether your pricing model is a model or just a hope. The invoice tells the client what they owe. WIP tells you whether the deal was ever any good.
Keep the timesheet. Attach every hour to a job. Watch committed effort against agreed fee. Bill when the work's done, not when someone remembers. That's not a return to hourly billing — it's the discipline that makes fixed fee profitable instead of merely simple.