Time-and-materials billing charges a client for the actual hours worked at an agreed hourly rate, plus the cost of materials used, typically with a markup added. Contractors turn to this model when a project's scope is uncertain or likely to change, since it avoids locking in a price before the full picture is known. This guide walks through the contract language, the billing math, and the operational habits that keep a T&M job profitable and dispute-free.
TL;DR:
- Round each time entry to the contract’s stated increment before multiplying by the hourly rate; weekly totals can otherwise diverge from timesheets.
- Use T&M for uncertain scopes or unknown site conditions; choose fixed price for documented work, or add a ceiling when clients need budget limits.
- Define billable activity, labor categories and rates, material markup, rounding increments, payment terms, change approvals, travel rules, and audit rights in the statement of work.
- Weekly or biweekly invoices, supported by timesheets, receipts, and change order records, surface disputes sooner and keep cash flow steadier than monthly billing.
Table of Contents
- What is time-and-materials billing: components and terminology
- How T&M billing works: time capture, increments, and invoicing
- When to use T&M billing on a project
- Contract contents checklist for a T&M statement of work
- Billing calculation examples and rounding rules
- Advantages and disadvantages of T&M billing
- How T&M compares with fixed-price, GMP, cost-plus, and labor-hour contracts
- Government and regulatory considerations for T&M contracts
- Practitioner note: running T&M billing with integrated tools
- Three rules I follow on every T&M job
- Running T&M billing without the spreadsheet headaches
- FAQ
- Sources
What is time-and-materials billing: components and terminology
A time-and-materials, or T&M, arrangement bills a client for labor and materials separately rather than for a lump sum. Getting the terminology straight prevents confusion later, both internally and with clients.
- Billable hours: time spent on client-facing work that gets charged, as opposed to internal tasks like training or administration.
- Labor category: a role classification (foreman, journeyman, apprentice, specialist) that typically carries its own hourly rate.
- Hourly rate: the fixed price charged per hour for a given labor category, agreed before work begins.
- Materials and markup: the cost of supplies or equipment, often marked up a set percentage to cover handling and procurement.
- Reimbursables: travel, permits, or other out-of-pocket costs passed through to the client.
The invoice totals $680 in labor and $460 in materials, before any reimbursable expenses.
How T&M billing works: time capture, increments, and invoicing
Accurate T&M billing depends on habits built into daily workflow, not end-of-month reconstruction. The process generally follows a few consistent steps.
- Capture time as it happens. Workers log hours contemporaneously, tagged by task and job, rather than estimating at the end of the week.
- Separate billable from non-billable activity. Training, internal meetings, and administrative work get tagged differently from client-facing tasks so invoices and utilization reports stay accurate.
- Round each entry individually. Most shops use 0.1-hour (6-minute) or 0.25-hour (15-minute) increments, rounding every single time entry before it gets multiplied by the hourly rate.
- Assemble the invoice on a set cadence. Weekly, biweekly, or monthly cycles each work, but shorter cycles tend to surface disputes earlier and keep cash flow steadier.
- Attach supporting documentation. Timesheets, material receipts, and change-order records should ride along with every invoice.
Rounding order matters more than most contractors realize. Rounding each individual time entry before multiplying by the hourly rate is the practice that prevents invoice totals from drifting away from the underlying timesheets.
Pro Tip: Round at the entry level, never after totaling the week, or your invoice and your timesheet will quietly stop matching.
When to use T&M billing on a project
T&M fits best when nobody, including the client, can fully define the scope before work starts. The commercial model should match the level of uncertainty on the ground.
- Favors T&M: exploratory or investigative scope, frequent change orders, unknown site or existing conditions.
- Favors fixed-price or guaranteed maximum price (GMP): a well-documented scope with stable drawings and specifications.
- Favors a hybrid: clients who want flexibility but still need budget certainty, which usually means pairing T&M with a not-to-exceed (NTE) ceiling.
Choosing the wrong model up front creates friction later. A client expecting a fixed number will push back hard on a T&M invoice that grows with discovered conditions, even when the work was legitimate.
Contract contents checklist for a T&M statement of work
A T&M agreement holds up under scrutiny when it spells out the mechanics in writing rather than assuming common understanding. Build the statement of work around these elements.
- Labor categories and fixed hourly rates, listed by role so there is no ambiguity about who bills at what rate.
- Definition of materials and markup percentage, including how handling and procurement costs get allocated.
- Invoicing cadence and required backup, specifying whether timesheets, receipts, and change-order records must accompany each bill.
- Payment terms, including due dates and any late-payment provisions.
- Not-to-exceed or ceiling price, capping total exposure if the client needs budget certainty.
- Change-order procedures, describing how scope additions get approved and billed.
- Travel and subsistence rules, clarifying whether windshield time or per diem gets charged.
- Audit rights, allowing the client to review time and material records on request.
The clause most disputes trace back to is the definition of billable activity. Spell out exactly what counts as chargeable time, and state the rounding increment in plain language so nobody is surprised by a 0.1-hour versus 0.25-hour difference months into the job.
Billing calculation examples and rounding rules
The core formula behind every T&M invoice is simple: rounded billable hours multiplied by the billing rate, plus material costs, plus any reimbursable expenses. The complexity lives entirely in the rounding step.
Consider a 22-minute task billed at $150 per hour. Rounded to the nearest 0.1-hour increment, 22 minutes become 0.4 hours, producing a $60 charge. Rounding happens at the entry level before any multiplication, not after hours get totaled for the week.
A 22-minute task rounds to 0.4 hours, and at $150 per hour that produces a $60 charge when rounded by entry rather than by total. Display material line items separately from labor, with the markup percentage shown rather than buried, so clients can see exactly what they are paying for.
Advantages and disadvantages of T&M billing
T&M billing trades price certainty for flexibility, and that trade cuts both ways depending on who is holding the risk.
- Advantage: work can start before the scope is fully defined, which speeds up mobilization.
- Advantage: scope changes get absorbed into ongoing billing instead of requiring a full contract renegotiation.
- Disadvantage: clients sometimes perceive T&M as lacking an efficiency incentive, since the contractor gets paid regardless of pace.
- Disadvantage: the administrative load of tracking, categorizing, and documenting every hour is heavier than a lump-sum job.
Mitigate the downsides with an NTE ceiling, a tightly written SOW defining billable activity, and interim progress reports tied to each invoice so the client sees value accumulating in real time.
How T&M compares with fixed-price, GMP, cost-plus, and labor-hour contracts
Understanding the alternatives helps explain to a client why T&M is, or is not, the right fit for their job.
- Fixed-price: the client gets full price certainty, but the contractor absorbs the risk of an inaccurate estimate.
- Guaranteed maximum price (GMP): a hybrid model with an upper cap, often including a shared-savings mechanism if actual costs come in under budget.
- Cost-plus: the client reimburses actual costs plus a fee, similar to T&M but typically structured around overall project cost rather than itemized hourly rates.
- Labor-hour: functions like T&M but excludes materials entirely, billing only for labor.
Each model shifts risk differently between contractor and client, which is why the scope certainty of a given job should drive the choice rather than habit or convenience.
Government and regulatory considerations for T&M contracts
Federal T&M contracts carry specific requirements that go beyond standard private-sector practice. FAR 16.601 requires a ceiling price and separate fixed hourly rates covering wages, overhead, general and administrative expenses, and profit for each labor category.
- A contracting officer must determine that no other contract type is suitable before a T&M agreement gets executed.
- The contract must include a ceiling price that the contractor exceeds at its own risk.
- Government surveillance is required because T&M contracts do not carry a built-in incentive for cost control the way fixed-price work does.
Federal T&M contracts require fixed hourly rates that separately account for wages, overhead, G&A, and profit by labor category, as specified under 48 CFR 16.601. For contractors bidding government work, that means rate schedules and indirect cost allocations need to be audit-ready well before the first invoice goes out.
Practitioner note: running T&M billing with integrated tools
Manual spreadsheets make entry-level rounding and documentation easy to get wrong, especially across multiple crews and jobs. Software that links time capture directly to job-level costs removes the gap between what a worker logs and what an invoice shows, and surfaces margin slippage before a job closes rather than after. When evaluating any platform for this, check for entry-level rounding support, a clear audit trail, invoice attachments for receipts and timesheets, and live margin reporting tied to each job.
Three rules I follow on every T&M job
Three habits save more margin than any contract clause: define billable tasks in writing before work starts, require contemporaneous time capture instead of end-of-week guessing, and tie interim progress reports to every invoice so the client never feels surprised. When change orders start piling up faster than the original SOW anticipated, that is usually the signal to renegotiate toward a fixed-price or GMP structure for the next phase.
— Ricky
Running T&M billing without the spreadsheet headaches
We built software to connect the pieces that make T&M billing accurate: time capture tied to each job, invoice assembly that pulls labor and material lines automatically, and tools that flag margin slippage while a project is still running instead of after the final invoice. For contractors juggling multiple crews and jobs at once, that integrated view replaces the reconciliation work that spreadsheets and disconnected tools leave behind.
Our TradePilot Monthly plan runs $175 per month, and you can explore the features that support job-level cost tracking before deciding if it fits your crew.
FAQ
What is the T&M billing model?
The time-and-materials (T&M) billing model charges a client for actual labor hours at agreed hourly rates plus the cost of materials, usually with a markup. It works best on projects where the scope is not fully defined before work begins.
How do you charge for time and material?
You multiply rounded billable hours by the agreed hourly rate for each labor category, then add material costs plus any applicable markup and reimbursable expenses. The formula is rounded hours times rate, plus expenses, with rounding applied to each entry before the multiplication.
What does "time and material costing" mean?
Time and material costing refers to tracking the actual labor hours and material expenses consumed by a project, then pricing an invoice directly against that consumption rather than a predetermined lump sum. It requires clear categorization of billable versus non-billable time to stay accurate.
Can you give an example of a time-and-materials contract?
A typical T&M contract lists labor categories with fixed hourly rates (say, $85 for a journeyman and $45 for an apprentice), a materials markup percentage, an invoicing cadence, and a not-to-exceed ceiling. It also defines what counts as billable work and states the rounding increment used for time entries.
When should a contractor choose T&M over fixed-price?
T&M fits best when scope is uncertain, site conditions are unknown, or change orders are likely, since it avoids locking in a price before the full picture is clear. Fixed-price works better when the scope is stable and well documented from the start.
Sources
- eCFR :: 48 CFR 16.601 -- Time-and-materials contracts.
- Ironclad: Time-and-materials contract (practitioner note)