FTE, and What It Hides
Why the full-time equivalent is the most convenient unit and the most misleading, the four things it conceals, and when to use it anyway.
The full-time equivalent is the unit most plans are written in, because it is the unit budgets are written in. It is also the unit that conceals the most, and the concealment is systematic rather than random: it always points the same way, towards optimism.
The unit used in “FTE, and What It Hides” must remain stable from capacity estimate to actual result. For organisations assessing a transparent fte meaning process in relation to fte meaning, time and project reports can support that reconciliation, provided leave, support work and corrections retain their own definitions.
The problem is not the arithmetic. One FTE is a defined quantity and the definition is usually written down somewhere. The problem is everything the definition leaves outside itself.
Additional context for “FTE, and What It Hides” is available from Stanford operations and technology resources. Use external material to prompt a specific validation check rather than replace local judgement.
What one FTE is defined as
A contractual quantity: one person working their full contracted hours for the period. That is all it asserts. It says nothing about whether those hours are available for planned work, and nothing about what the person can do.
- Contracted hours. The figure in the employment contract, before anything is deducted.
- Paid hours. Contracted, less unpaid absence. Closer to payroll's view and usually what a headcount budget means.
- Available hours. Paid, less leave, holidays, sickness and training. What a scheduler can see.
- Productive hours. Available, less support and interrupts. What the plan can actually spend.
Everything else attributed to an FTE — productivity, skills, availability — is an assumption layered on top by whoever is reading the plan.
The first thing it hides: availability
An FTE includes leave, training, sickness, support duty and every other claim on the person's time unless somebody has explicitly netted those off. In most plans nobody has.
The result is a unit which claims a quarter of 520 hours and delivers somewhere between 300 and 470 depending on the organisation. The difference is not noise; it is the subject of the next section of this collection.
The second thing it hides: shape
Two half-time people are one FTE and are not one person. They cannot cover a shift between them without handover, they attend the same meetings twice, and each has their own leave, their own training and their own ramp.
Where a plan is sensitive to continuity — anything with handover, with customer relationships, with deep context — the FTE is the wrong unit and the error is invisible in the total.
The third thing it hides: capability
An FTE of a person who can do the work and an FTE of a person who cannot are the same number. Plans that are short of a specific capability routinely show as adequately resourced, because the shortage is in the composition and the unit does not carry composition.
This is the same failure as counting headcount instead of skill mix on a rota, arriving from the demand side instead of the supply side.
The fourth thing it hides: the ramp
A person who joins in week three of the quarter is not 0.77 FTE of useful capacity. They are considerably less, for a period that depends entirely on the work, and then they are more than they were.
Plans that pro-rate new joiners by calendar time produce a specific, repeatable over-estimate, and it is the easiest of the four to correct.
When to use it anyway
For budgeting, for headcount approval, and for any conversation where the counterparty thinks in posts rather than in hours. The FTE is the lingua franca and refusing to speak it is a way of not being understood.
The discipline is to convert at the boundary: speak FTE outward, hold hours inward, and state the conversion factor on the page.
The conversion factor as policy
Whoever sets that factor sets how optimistic every plan in the organisation is. Setting it at contracted hours makes every plan optimistic by the shrinkage rate; setting it at measured net hours makes every plan honest and every budget look worse.
That is a real decision with real consequences and it is almost never taken deliberately. It is inherited from whatever the spreadsheet did.
The half-person problem
Plans expressed in FTE accumulate fractions — 1.5 here, 0.8 there, 0.25 for a support rota — and fractions of a person cannot be allocated. Somebody ends up on three things at once.
Converting to hours makes the fragmentation visible, which is uncomfortable and correct. A person split four ways loses time to the splitting, and the hours account can show that where the FTE account cannot.
The two plans that disagree by a third
A useful exercise on any existing plan: write the same quarter twice, once in FTE at contracted hours and once in available hours, and put the two totals side by side.
The second is usually between twenty and forty per cent smaller. That difference has been inside every plan the organisation has published, and nobody has ever been shown it as a single number.
Where the unit does real harm
In commitments. An FTE given to a sponsor as a promise is heard as a person who will be there, and delivered as a fraction of several people net of everything in this page.
The gap between those two readings is where most resourcing disputes start, and it is entirely a unit problem rather than a performance one.
What to write beside the number
Whenever an FTE figure appears in a plan: what it is net of, what the conversion factor is, and whether it includes the ramp for anybody who started recently.
Three short clauses. They do not make the unit better; they stop it being read as something it never claimed to be.