Every contractor reaches for time and materials when the scope is too fuzzy to price. A water-damage repair behind a wall. A remodel where the client keeps adding ideas. A service call that could be 90 minutes or could turn into a two-day rebuild. The logic is simple — you can’t lose money if you bill what you actually spend.

Except that’s not what happens. Talk to ten contractors who run T&M work and most will tell you the same thing: their fixed-price jobs hit margin more reliably than their T&M ones. The reason isn’t the contract type. It’s that T&M shifts the burden of proof onto the contractor, and most contractors aren’t built to carry it.

Why T&M Bleeds Margin Even When You Think You’re Winning

Fixed-price work forces discipline at the front end. You estimate, you commit, you track against the number. T&M removes that pressure and replaces it with a different one: every hour, every receipt, every markup decision has to be defensible at invoice time. If you can’t produce the paper, you eat the cost.

The leaks are predictable. Field crews forget to log the first 45 minutes of a shift because they were “just looking at it.” A laborer drives to the supply house twice in one day and only one trip ends up on the ticket. Small consumables — blades, fasteners, drop cloths — vanish into general overhead because nobody wants to itemize $14 of screws. Each leak is tiny. Across a quarter of T&M work, they add up to the entire profit margin.

The trap of T&M isn’t the contract. It’s that the contract assumes a level of administrative discipline most small contractors haven’t built into their daily routine.

The Rate You Charge Is Not the Rate You Think You’re Charging

Most contractors quote a labor rate that covers wages plus a comfortable markup, and forget that the “wages” number on the W-2 is not what an hour of labor costs them. Once you add payroll taxes, workers’ comp, general liability allocation, vehicle and tool depreciation, paid time off, and supervisor overhead, your fully-burdened cost on a $28/hour carpenter is closer to $42–$46.

If you billed that carpenter at $65 thinking you had a 130% markup, you actually have a 41%–55% gross margin — and after non-billable time (travel, paperwork, callbacks) the contribution to overhead and profit might be 25%. That’s before the materials side starts leaking too.

A defensible T&M rate sheet has three columns the contractor sees and one the client sees. Internal columns: base wage, burden, target margin. Client-facing column: the single billable rate. Build the math once, lock it for the year, and stop letting field supervisors quote off-the-cuff rates to win quick work.

Materials Markup: The Number Everyone Underprices

Industry surveys put materials markup on T&M work anywhere from 10% to 35% depending on trade and region. Most small contractors land at 15%, which sounds reasonable until you actually price what materials handling costs you.

  • The pickup run — an hour of crew time, a truck, fuel, and the opportunity cost of not being on site billing.
  • Will-call and returns — the wrong fitting, the cracked tile, the back-ordered window that takes three calls to chase.
  • Stocking and storage — the shop or trailer where materials sit between purchase and install.
  • Carrying cost — you paid the supplier in 15 days; the client pays you in 45.
  • Damage and shrinkage — the saw blade that got left in the rain, the box of trim somebody walked off with.

Add those up honestly and a 15% markup barely covers the handling cost, never mind generating margin. Tradespeople with strong margins on T&M typically run 20%–28% on materials and write it into the contract before signing. The client doesn’t flinch if it’s disclosed up front. They riot if it appears as a surprise on the invoice.

Documentation Is the Whole Job, Not an Afterthought

On fixed price, paperwork is overhead. On T&M, paperwork is the product. The hours you billed don’t exist until you can show what was done in them. The materials you bought don’t exist until you can show the receipt and tie it to the job.

Three documentation habits separate the contractors who hit T&M margin from the ones who hope:

  • Same-day time entry — not Friday afternoon, not Sunday night. Hours logged more than 24 hours after the work are reconstructed, and reconstructed hours are systematically undercounted by 8–15%.
  • Per-job receipt capture — a phone photo of every receipt, tagged to the job number, taken before the receipt leaves the supplier’s parking lot. The folder of crumpled tickets in the truck console is where margin goes to die.
  • Daily field notes — a short paragraph per crew per day on what was done, weather, delays, client conversations. This is what you produce when the client questions hours three weeks later.

The contractors who do this aren’t more organized by nature. They’ve just made it impossible to skip. Phone capture, app-based time entry, a daily reminder that fires at 4:30 pm. Tools like TrestleBook are built around this loop — punch in, log materials, snap the receipt, push the day’s entries to the invoice with the job already tagged — specifically because the manual version of this workflow gets skipped by the third week of any job.

Ready to put this into practice? Download TrestleBook Free — it’s free and works offline.

The Not-To-Exceed Clause That Quietly Eats You

Clients who’ve been burned by open-ended T&M ask for a not-to-exceed (NTE) cap. Contractors who want the job agree, often without thinking through what NTE actually means under their own paperwork.

Here’s how it goes wrong. You agree to T&M with an NTE of $18,000. At hour 60 you’re tracking toward $22,000 because of conditions you couldn’t see at quote time. You keep working — you have to finish — planning to negotiate the overage at the end. The client refuses to pay above the cap. You eat $4,000.

An NTE without a change-order trigger is a fixed-price contract wearing a T&M costume. You take the documentation burden of T&M and the cap risk of fixed price.

The fix is structural, not interpersonal. Write into the agreement that work pauses at a defined percentage of NTE — typically 75% — pending a written change order if projections show overage. Then build a habit of checking job-to-date cost against NTE at least weekly, not at the end. Most contractors find out they’ve blown the cap a week after they could have stopped.

Mixing T&M and Fixed Price on the Same Job

Real jobs rarely fit neatly into one contract type. The kitchen remodel might be fixed price for the demo, cabinet install, and finish work, but T&M for the unknown electrical behind the old plaster. Combining the two is fine. Letting them blur is not.

Two practical rules. First, write distinct sections in the contract for each — what’s included in fixed scope, what triggers T&M, what rate sheet applies, what NTE governs the T&M portion. Second, code time and materials to the right bucket on the day they happen. Crews working a fixed-price wall on Tuesday and chasing T&M electrical on Wednesday need to know which job code they’re on. The contractor who codes everything to one job number and tries to split it at invoice time always splits it wrong — almost always against themselves.

This kind of job costing discipline isn’t unique to construction. Freelancers and consultants running hourly engagements face the same exact failure modes — tools like Stintly exist for the same reason field-focused tools do: the hour you forget to log is the hour you don’t bill. Same instinct, different vertical.

Client Communication Is Where T&M Margin Is Actually Won

The technical side of T&M billing is solvable in a week of habit changes. The relational side is what separates contractors who renew with T&M clients from ones who collect a final check through gritted teeth.

Clients on T&M get nervous because the meter is running and they can’t see it. The contractor who waits until invoice day to surface the number is delivering a $14,000 surprise to someone who was bracing for $9,000. That conversation rarely ends with full payment on time.

  • Weekly running totals — a short email or text every Friday with hours logged, materials spent, and projected to completion. Boring, undramatic, and the single biggest predictor of full collection.
  • Surface scope creep the day it happens — “You asked about adding the pantry shelving — that’ll add about four hours and $180 in material at our T&M rate. Want me to proceed?” Written confirmation, same day.
  • Walk the work weekly — client on site, you on site, run through what was done and what’s next. Hours billed against work the client has seen and acknowledged don’t get challenged later.

The same logic applies to anyone billing time against someone else’s asset — landlords managing rental turnover, for instance, face the same “why was this $1,400 for a repair” conversation, and tools like KeyLoft exist partly to keep those records straight before the dispute, not after. Documentation prevents the argument; it doesn’t win the argument.

What a Disciplined T&M Workflow Actually Looks Like

Strip away the theory and the day-to-day looks like this. Before the job starts: signed agreement with rate sheet, materials markup percentage, NTE with change-order trigger at 75%, scope of what counts as T&M versus fixed. During the job: same-day time entry per crew member per job code, receipts photographed and tagged on the spot, daily field notes, weekly client update with running total. At job close: invoice within seven days while memory is fresh, with itemized hours, materials with markup shown as line item, and a one-page job summary attached.

None of that is exotic. It’s the floor. The contractors who treat it as the floor charge more, collect faster, and stop dreading T&M jobs. The ones who treat documentation as something to do later end up rebuilding invoices from receipts, memory, and guesswork — and the guesswork is always too generous to the client. TrestleBook was built to compress this loop down to a few taps per day, because the workflow on paper is the difference between margin and a polite write-off.

Time and materials isn’t inherently riskier than fixed price. It’s differently risky. Fixed price punishes bad estimating up front. T&M punishes bad bookkeeping every single day until the job closes. Pick the contract that matches the scope clarity — and then run the back-office discipline that contract actually demands. Skip the second part and you’ll keep wondering why the “safer” jobs are the ones leaving you light.