Flat Rate vs Time and Materials: The Break-Even Math

How each model is built

Time and materials (T&M) bills the hours actually worked at an hourly rate, plus materials. Federal contracting rules give a clean, neutral definition: FAR 16.601 describes a time-and-materials contract as labor hours at fixed hourly rates that already include wages, overhead, general and administrative expense and profit, plus materials at actual cost.

Those rules govern government contracts, not residential service work, but the structure is the same one a trade shop uses. ShiftFlow, a software vendor, describes trade T&M as the hourly rate plus marked-up parts. Whether you mark up parts is your call; this guide does in both models so the comparison is fair.

Flat rate gives the customer one price for a defined task before work starts. The site's flat-rate calculator builds it like this:

price = standard hours × hourly rate + materials × (1 + markup) + callback allowance, rounded up

Standard hours are your shop's own average time for that task. The hourly rate is the one from the labor rate calculator, which already carries labor burden, overhead, the truck and net profit. So no separate overhead line goes on top. If a formula you come across adds an overhead allocation to a fully loaded rate, and your rate already includes overhead, that formula counts it twice.

Both models use the same rate. What differs is which hours get billed (actual or standard), who carries the time risk, and where the money for callbacks comes from.

The federal rules spell out that risk split too. FAR 16.202-1 says a firm-fixed-price contract places on the contractor "maximum risk and full responsibility for all costs," and with it the strongest reason to control them. FAR 16.601 notes that a T&M contract gives the contractor no positive profit incentive for cost control or labor efficiency. Roto-Rooter, a plumbing company describing its own pricing, puts it in shop terms: with flat rate the plumber takes the time risk, and with hourly billing the customer does.

The example shop's numbers

The worked examples use the example shop behind the site's labor rate calculator:

• Billable rate: $125.20 an hour, which includes a 10% net profit on price
• Loaded labor cost: $66.07 per billable hour
• Overhead and truck: $46.61 per billable hour ($32.87 + $13.74)
• Full cost of one hour on a job: $112.68, the break-even rate

That rate assumes 65% of worked hours are billable. The figure comes from a report by Field Promax, a software vendor, covering 300 HVAC companies, as reported by ACHR News. The report measured 65% as a share of paid time; applying it to worked hours, as the calculator does, gives fewer billable hours and a higher rate. It is one company's sample of HVAC shops, not an official statistic, and it says nothing direct about plumbing or electrical crews. Use your own ratio when you run your numbers.

The same job priced both ways

Take one repeatable task. Your tickets say it averages 1.5 hours on site, the parts cost you $85, you mark parts up 50%, and you set a 2% callback allowance. All four numbers are examples.

The flat price:

• Labor: 1.5 × $125.20 = $187.80
• Parts: $85 × 1.50 = $127.50
• Subtotal: $315.30
• Callback allowance: 2% × $315.30 = $6.31
• Total: $321.61, rounded up to $322

The T&M price is the actual hours × $125.20, plus the same $127.50 of parts. Here is what each model brings in, and keeps, as the actual time changes:

Job cost is what the job costs the shop: the $85 of parts plus every hour at the $112.68 full cost, the same method the job cost calculator uses. Net profit is price minus job cost, before any callback.

Two patterns stand out. Under T&M, each extra hour adds $12.52 of profit, the 10% profit built into the $125.20 rate, so the job can't lose money as long as every hour gets billed. Under flat rate, each extra hour takes away the full $112.68. Flat rate earns far more on a fast job and loses on a slow one.

Where the two models break even

Three numbers from that table tell you most of what you need to know.

• Price crossover: 1.55 hours. (322 − 127.50) ÷ 125.20 = 1.5535. On a job that finishes faster, the flat-rate customer pays more than the clock would have charged. On a slower job, the customer pays less.
• Flat-rate zero-profit point: 2.10 hours. (322 − 85) ÷ 112.68 = 2.1033. Past that, the flat price no longer covers the job's full cost.
• At standard hours, flat rate earns a little more. At exactly 1.5 hours, the flat price makes $67.98 against $61.28 under T&M. The $6.70 gap is the $6.31 allowance plus $0.39 of rounding. That money is set aside for callbacks; it isn't extra profit. After setting the allowance aside, the $322 price earns a 19.53% net margin on full cost, the figure the flat-rate calculator reports for this example.

Another way to read the same numbers is the hourly rate the flat price actually earns. Take the $127.50 of marked-up parts out of $322 and $194.50 is left for labor.

On a 1-hour job, that's $194.50 an hour. On a 2-hour job, it's $97.25 an hour, already below the $112.68 an hour that a job costs the example shop. The flat price never changes, but the rate it pays you does, every time the clock runs.

The distance between standard hours and the zero-profit point is your cushion. Here it is 0.60 hours, about 36 minutes.

The parts markup does a lot of that work. A labor-only task priced the same way at 1.5 hours comes to $192 and stops paying at 1.70 hours, a cushion of about 12 minutes. Labor-heavy tasks need the most accurate standard hours.

What happens across many jobs

One job tells you little; flat rate is an average across many. Say your last twelve jobs of this task took 1.2, 1.5, 1.4, 1.1, 1.8, 1.3, 1.6, 1.5, 2.2, 1.4, 1.3 and 1.7 hours (an example history). That is 18.0 hours in total, an average of 1.50 hours and a median of 1.45.

The $80.40 difference is 12 × $6.70, the allowance and rounding again. When standard hours match the true average, the two models bring in nearly the same money across many jobs. Flat rate just spreads the time evenly across customers. The 1.1-hour customer paid $322 instead of $265.22; the 2.2-hour customer paid $322 instead of $402.94, and that one job lost the shop $10.90.

The real risk is bad standard hours. If this task actually averages 1.75 hours and the book says 1.5, the flat price earns $39.81 a job against $64.41 under T&M: $24.60 less on every job, or $295.20 over twelve. That's why standard hours have to come from your own tickets. The site publishes no task times, and any time copied from someone else's book carries their crew, their trucks and their market.

Callbacks and warranty work

A callback costs you under either model; the two handle it differently. Under T&M, there is nothing in the price for returns unless you bill the return trip or carry the cost in overhead. Under flat rate, the site's convention is a callback allowance: a percentage added to each price to pay for the returns you expect.

The arithmetic is simple: allowance ≈ callback rate × (average callback cost ÷ average ticket). Say 4 of every 100 jobs of this task come back, and each return takes 1.25 hours at the $112.68 full cost, or $140.85. Then 0.04 × 140.85 ÷ 315.30 = 1.79%, and rounding up gives the 2% used above. The 4-in-100 rate is an example.

No source used for this site gives a typical callback rate for plumbing, HVAC or electrical work. So the flat-rate calculator's default allowance is 0%, and the number has to come from your own records. Track returns by task. A task that keeps coming back needs a better scope or more hours, not just a bigger allowance.

How customers see each price

With flat rate, the customer sees one number before work starts. Roto-Rooter describes its process this way: the plumber assesses on site, quotes the job, starts only after the customer accepts, and keeps the price whether the job turns out simpler or harder. It also says anything found outside the quoted scope gets a separate quote. That's why a written scope matters as much as the price.

With T&M, the customer carries the time risk and pays less for a fast job. The flip side shows in the twelve-job example: under flat rate, the quick-job customer paid more than the clock would have charged. Present a flat price as the price of the job, not of the hour. If a customer asks how long it will take, give your best time estimate and say the price doesn't change with it.

The scope line does the heavy lifting in both directions. A tight scope protects the shop from absorbing work that was never part of the task. It also protects the customer from a price that grows mid-job. Write it so a tech can read it aloud in the driveway: what the price includes, what it leaves out, and what happens if the tech finds something else.

Vendors that sell price-book software, Workiz among them, claim flat rate brings faster approvals and healthier margins. Treat those as vendor claims. The math above shows that the profit depends on the standard hours being right.

After-hours pricing is a choice in either model. The Department of Labor says the Fair Labor Standards Act requires overtime pay for hours worked over 40 in a workweek, and doesn't require it for work on Saturdays, Sundays or holidays as such. That is general information about federal law; your state labor department or an employment attorney can tell you how it applies to your crew.

A 1.5 multiplier (an example) turns the $321.61 price into $482.41, or $485 rounded up to the next $5. Under T&M, the same choice shows up as an after-hours hourly rate.

When time and materials still fits

FAR 16.601 allows a T&M contract only when the extent or duration of the work can't be estimated with reasonable confidence. The same test works in a service shop.

• Work you can't see yet. ShiftFlow lists repipes, slab leaks and troubleshooting behind a wall as T&M work; Workiz also reserves T&M for jobs with unpredictable scopes.
• Tasks with no history. Until you have tickets showing how long a task takes, you have no standard hours to price from.
• Diagnosis first. A diagnostic or service-call fee, then a flat price for the repair once the problem is known. The service-call fee guide covers how to build that fee.
• T&M with a cap. Federal T&M contracts carry a ceiling price that the contractor exceeds at its own risk (FAR 16.601). A not-to-exceed figure on a residential estimate works the same way: it hands part of the time risk back to you, so set the cap from a realistic worst case, not the average.

ShiftFlow notes that many shops run both models: flat rate for the catalog of known tasks, T&M for genuine unknowns. Nothing in the math argues against that mix.

How to switch one task to flat rate

1. Pick one repeatable task. It should have a clear start and finish, come up often, and use a parts list that rarely changes.
2. Pull the actual hours. From the last 12 months of tickets for that task, list the on-site hours for each job. Note the outliers and why they ran long.
3. Set standard hours. Start from the average and compare it with the median and the slowest jobs. In the example history, the average is 1.50 hours, the median 1.45 and the slowest job 2.2. Rounding up to the next quarter hour adds a cushion, but it raises the price for every customer. If one slow job had a clear cause, such as a seized valve or poor access, decide whether that belongs in the standard task or in a separate add-on entry.
4. Use your real rate. Take it from the labor rate calculator, and don't add overhead again.
5. Price parts at today's cost. Use your current supplier cost, including any sales tax you pay as the consumer of materials, times (1 + your markup).
6. Add the callback allowance from your own return rate, then round the total up to your price step.
7. Write the scope. List what's included, what's excluded, and what finding triggers a new quote.
8. Decide trip and after-hours handling. If you also charge a trip fee, don't bill the drive time a second time inside the flat price.
9. Check sales tax. In some states the contract type changes how sales tax applies to materials. California's CDTFA, for example, says a contractor is always the consumer of materials under a lump-sum contract and generally the consumer under a T&M contract, but becomes the retailer of materials when it bills the customer sales tax computed on marked-up materials (Publication 9). This is general information, not tax advice; ask your state revenue department or your accountant, and see do plumbers charge sales tax.
10. Run it, then review. Log actual against standard hours on every job for a set period, a quarter for example, and adjust the hours, the allowance or the scope. When you have several tasks done this way, the price book guide shows how to organize them.

Next step

Open the flat-rate price calculator and enter one task: your standard hours, your hourly rate, the parts cost, your markup and your callback allowance. Read the net margin line before you print the price: it shows what the rounded price earns on full cost. Then run the zero-profit check from this guide, (price − parts cost) ÷ full cost per hour, to see how long the job can run before the price stops paying.