Billing Models Explained

What Is Time and Materials Billing?

Time and materials billing reimburses documented labor at agreed hourly or daily rates and passes through materials (plus an agreed markup when allowed). It fits work where the scope, duration, or material list is hard to price upfront. Pair it with written rates, approval rules, and either milestone billing or a not-to-exceed cap so totals stay predictable.

Quick reference

Time and materials and close cousins

Use these definitions with clients and accounts payable so rates, receipts, and caps mean the same thing on every bill.

What is time and materials billing?

Time and materials billing is an invoicing model that charges for qualified labor time at preset rates and adds the cost of materials (and sometimes equipment or subs) that the contract allows. It is common in repair work, professional services, creative agencies, IT support, and construction tasks where discovery is still open.

  • Rates are fixed in the agreement even when total hours are not
  • Materials tie back to receipts or vendor bills you can show on request
  • Totals move with actual effort, so scope control and approvals matter
  • Works well when paired with clear change rules and billing cadence

Example

A facilities vendor responds to an emergency leak. The work order lists $135 per hour for a technician, $95 per hour for a helper, and materials at supplier invoice plus 12 percent. The weekly invoice shows dated time entries and scanned receipts.

How does fixed price differ from T&M?

Fixed price billing sets one total (or clear milestone totals) for a defined scope. The seller carries more cost risk if work runs long, while the buyer gets price certainty. Many teams move from a T&M discovery phase to a fixed quote once requirements stabilize.

  • Price stays the same unless a written change order adjusts it
  • Less weekly paperwork for the buyer than dense timesheets
  • Seller must manage margin inside the agreed total
  • Often follows an estimate or T&M discovery window

Example

A designer bills 20 T&M hours to map user flows, then issues a fixed $18,000 quote for the full UI build. Invoices after that match the quote or approved change orders, not hourly sheets.

What is a not-to-exceed amount on T&M work?

A not-to-exceed cap is a ceiling written into the agreement. You may still bill time and materials underneath it, but you need a signed change order before you exceed the cap. Caps reduce buyer anxiety while keeping T&M flexibility for unknowns.

  • Creates a hard stop unless both sides approve more budget
  • Requires tracking burn against the cap on every invoice
  • Common on government-style and enterprise purchase orders
  • Pairs well with weekly or biweekly billing so surprises surface early

Example

A software consultant agrees to $12,000 NTE for a migration assessment. They invoice $140 per hour plus pass-through cloud charges until they near the cap, then stop or request a written extension.

Side-by-side

Time and materials vs fixed price vs not-to-exceed

T&M bills what actually happened. Fixed price bills what you promised for a defined scope. Not-to-exceed is T&M with a safety rail. Pick the model that matches how uncertain the work is and how much proof your client needs.

Best when

Time and materialsScope, hours, or materials are still moving
Fixed priceDeliverables and exclusions are already clear
Not-to-exceed (T&M + cap)Buyer wants flexibility but not an open checkbook

Price certainty for the client

Time and materialsLow until you add a cap or milestone plan
Fixed priceHigh when change orders are disciplined
Not-to-exceed (T&M + cap)Medium: they know the worst case if they do not expand the cap

Typical paperwork

Time and materialsTimesheets, rate cards, receipts, approvals
Fixed priceQuote, milestone acceptance, fewer line updates
Not-to-exceed (T&M + cap)Same as T&M plus a running cap tracker

Who bears overrun risk

Time and materialsBuyer pays more if work expands
Fixed priceSeller eats extra cost unless scope shifts
Not-to-exceed (T&M + cap)Seller stops at the cap unless both sides agree to raise it

Cash timing

Time and materialsOften billed weekly or biweekly as hours land
Fixed priceOften milestone or percent complete
Not-to-exceed (T&M + cap)Same as T&M, with extra focus on burn pacing

Common pairing with documents

Time and materialsEstimate or rate sheet, then T&M invoices
Fixed priceQuote or statement of work, then milestone invoices
Not-to-exceed (T&M + cap)Purchase order with cap, then T&M invoices to the limit

Practical guidance

When to use time and materials billing

Use T&M when honest pricing requires measuring the work as you go. Move to fixed price when you can define scope tightly. Add a not-to-exceed cap when the buyer needs a ceiling while you still need flexibility.

Time and materials first

Choose T&M when discovery, site conditions, or stakeholder input can change the path.

  • Support tickets, break or fix work, or short urgent repairs
  • Creative or engineering phases where rounds of review move hours
  • Construction or field services with unknown hidden conditions
  • Software discovery when integrations and data quality are still opaque

Publish rates, rounding rules, and minimum increments (for example 15 minutes) before the first hour hits the invoice.

Shift to fixed price

Move to a lump sum once you can list deliverables, deadlines, and exclusions without hand waving.

  • Repeatable packages you have costed many times
  • Regulated scopes with stable specifications
  • Competitive bids that require a single number
  • When the client insists on budget certainty over flexibility

Carry line items and totals forward from the accepted quote so the invoice matches what they approved.

Add a not-to-exceed cap

Use a cap when procurement needs a ceiling but hourly detail is still the fairest way to bill.

  • Enterprise or municipal buyers with hard PO limits
  • Pilot projects that may stop early if results disappoint
  • Mixed teams where subs and materials fluctuate week to week
  • When you want T&M mechanics without unlimited exposure for the client

Show remaining cap on each invoice header so approvers see burn without opening a spreadsheet.

What sets them apart

Key differences you should spell out in writing

T&M arguments usually trace back to unclear rates, missing receipts, or silent assumptions about markups. Fixed price disputes often trace to scope drift. Name the rules up front and you avoid both flavors of conflict.

Rates versus totals

T&M lives in rate cards and auditable time. Fixed price lives in scope documents and milestone acceptance. If you blend models, say which parts are hourly and which parts are lump sum so accounts payable codes them correctly.

Materials and markup

State whether materials are at cost, cost plus an agreed percent, or list price from your catalog. Note whether sales tax passes through and whether rush shipping is reimbursable. Silence here invites rework of invoices.

How this connects to quotes and estimates

Estimates give a range before details firm up. Quotes lock a fixed path. T&M invoices collect what happened when the path could not be locked early. For a full walkthrough of the document sequence, see our glossary on invoice versus quote versus estimate.

Payment terms still matter

T&M does not replace net 30 or other due date rules. It only describes how dollars add up. Put your term, due date, and discount logic on every bill so finance teams can schedule payment. Our net 30 glossary page shows how to phrase those lines clearly.

Collections discipline

Marco Carbajo, an SBA blog contributor writing for the U.S. Small Business Administration, advises owners to "Issue invoices immediately and have a follow up system for collecting." That habit matters more when each invoice total can move with new hours and receipts.

Workflow

How to run a simple T&M billing workflow

Agree rates and markup rules, capture time and receipts as you go, review against any cap, then invoice on a steady cadence with terms that match your quote or master agreement.

  1. 1

    Lock the commercial skeleton before work starts

    Confirm labor categories, billing rates, markup on materials, reimbursable expenses, billing frequency, and any not-to-exceed ceiling. Put them in your master agreement, statement of work, or purchase order so later invoices have a single source of truth.

    Tip: If legal review is slow, use a signed rate schedule plus a short email recap rather than starting with a blank page.

  2. 2

    Set approval rules for extra spend

    Decide who can authorize overtime, rush shipping, or subcontractor pass through. Write whether verbal approval counts for your business and how quickly written confirmation must follow.

    Tip: For field crews, a one page checklist taped in the truck beats a policy nobody reads.

  3. 3

    Capture time and receipts in near real time

    Daily notes beat Friday guesses. Photos of supplier tickets beat lost paper. Tie each entry to a job code so invoices map cleanly to the client budget line they expect.

    Tip: If you round time, disclose the rounding in the contract and repeat it on the invoice footer.

  4. 4

    Review burn against caps before you overspend

    Each billing cycle, compare hours and materials to date with any NTE or phase budget. If you are on pace to breach, pause for a change order instead of surprising the client after the fact.

    Tip: A simple burn chart in your project tool is enough for many small teams.

  5. 5

    Invoice on schedule with transparent line items

    Group labor by role, list materials with vendor references, and show subtotals by category. Mirror the payment terms and due date language you use on other billing models so AP can treat the bill normally.

    Tip: Reference the PO number and cap remaining in the memo block if the buyer uses ERP matching.

  6. 6

    Follow up with the same rhythm as any receivable

    T&M totals may be new each cycle, but collection rules stay the same. Send reminders before the due date, document promises to pay, and escalate using the policy already in your agreement.

    Tip: Pair polite tone with specific invoice numbers and amounts every time.

Pitfalls

Common time and materials billing mistakes

Most T&M pain comes from fuzzy rates, missing backup, or caps that nobody tracked. Fixing those three items prevents the majority of disputes.

Starting work before rates are signed

Problem

You assume your standard rate card applies, while the client remembers a lower number from a verbal call. The first invoice shocks them.

Fix

Exchange a short written rate sheet or signed order before the first billable hour.

Markup surprises

Problem

You add 20 percent on materials without stating it in the agreement. Procurement rejects the invoice as out of policy.

Fix

Disclose markup or handling fees in the contract and repeat the rule on each invoice subtotal.

Loose time descriptions

Problem

Lines that say only meeting or project work give approvers nothing to audit. Payment stalls while they ask for detail.

Fix

Use plain English task labels, dates, and outcomes so a reasonable reviewer can see value.

Ignoring the cap until it is breached

Problem

You bill past a not-to-exceed ceiling without a change order. The client refuses to pay the overrun.

Fix

Stop at the cap, notify the sponsor, and document any written extension before more work.

Mixing T&M lines into a fixed quote without labels

Problem

The client thinks everything is fixed while you embedded hourly troubleshooting. Expect rework of the invoice and damaged trust.

Fix

Split phases in writing: fixed discovery workshop, T&M implementation, fixed training block, for example.

Checklists

Checklists for T&M agreements and invoices

Use these lists as a minimum. Tax, union, or agency rules may require more fields for your industry.

In the agreement or PO

  • Labor categories and billing rates, including overtime if it differs
  • How materials, equipment, freight, and subs are billed and marked up
  • Billing cadence and invoice delivery method
  • Any not-to-exceed ceiling and how to raise it
  • Record retention and audit rights if the client requires them

On each T&M invoice

  • Business identity, client AP details, and PO or contract reference
  • Unique invoice number, issue date, payment terms, and due date
  • Time entries with date, role, hours, rate, and line total
  • Materials with vendor, receipt reference, cost, and markup line
  • Subtotals, taxes if applicable, and grand total in the agreed currency

Internal controls

  • Someone who does not bill the hours still reviews long entries weekly
  • Receipt photos or PDFs filed next to the job record
  • Cap tracker updated before each new invoice batch
  • Written change orders logged before rates or scope shift
  • Collections notes stored with the invoice thread

Sources

Cash flow, surveillance, and records

T&M billing sits inside the same cash and compliance reality as any other model. These points cite neutral sources you can open for full context.

  • Federal Reserve analysis of the Small Business Credit Survey finds that roughly four in five small firms report challenges related to customer payments.

    Federal Reserve Banks, Small Business Credit Survey (2024). View source

  • The IRS lists invoices among supporting documents businesses should keep to show amounts and sources of gross receipts and to support entries on tax returns.

    Internal Revenue Service (2025). View source

  • The Federal Acquisition Regulation states that a time-and-materials contract provides no positive profit incentive to the contractor for cost control or labor efficiency, so appropriate government surveillance of contractor performance is required to give reasonable assurance that efficient methods and effective cost controls are being used.

    Federal Acquisition Regulation (FAR 16.601) (2026). View source

Related document types

Overtime, mixed crews, and sales tax on pass throughs

T&M shines on messy jobs, which means edge cases are normal. Decide them in writing once, then repeat the rule on invoices.

Overtime and double time

Say whether premium wage rates flow straight through to the client or are absorbed in your loaded billing rate. Public works and union jobs may have mandatory premiums you must disclose.

Materials sales tax

Some states tax your resale of materials differently than your labor. Say whether tax is included in your material line or added below. If you are not a tax advisor, point clients to their accountant for multi state deals.

Internal transfers between your own divisions

Large contractors sometimes move crews between subsidiaries. If your agreement mirrors federal practice, intercompany transfers may need special rate rules. Small businesses usually keep it simple by billing only the labor the client actually sees.

Frequently Asked Questions

Straight answers on time and materials billing, caps, invoices, and how T&M fits with quotes and payment terms.

What does time and materials billing mean?

It means you bill for qualified labor at agreed rates and add allowed materials and pass through costs, usually with receipts. Totals change with actual effort, so contracts should list rates, markups, billing cadence, and any not-to-exceed cap.

Is time and materials the same as hourly billing?

Hourly billing is usually the labor half of T&M. Full T&M also includes materials, equipment, subcontractor pass through, and sometimes travel, each governed by the contract. If you only bill hours, say hourly services so clients do not expect free materials.

How is T&M different from a fixed price contract?

T&M charges for what happened at published rates. Fixed price charges an agreed total for a defined scope even if you finish faster or slower. Many projects start T&M for discovery, then shift to fixed price once scope is clear.

What is a not-to-exceed cap?

It is a ceiling on T&M spend. You may bill up to the cap with normal time and material detail, but you need a written change order before you exceed it. Show remaining cap on invoices when buyers ask for it.

Should I use an estimate or a quote with T&M work?

Use an estimate when you are giving a range before rates and unknowns are settled. Use a quote when you can commit to a fixed package. With pure T&M, you often issue a rate sheet or small statement of work instead of a single lump price. See our invoice versus quote versus estimate glossary for the full document ladder.

How do net 30 terms work with T&M invoices?

Net 30 still means the buyer pays within thirty days from the agreed start date, usually the invoice date, unless the contract picks another trigger. T&M only changes how the amount is calculated, not how due dates work. Spell out the term and print the due date on every bill.

What should a T&M invoice include?

Include your business and client details, PO or contract reference, unique invoice number, dates, payment terms, labor lines with roles and hours, material lines with receipt references, any agreed markup, subtotals, tax lines if required, and the total due with payment instructions.

Can clients dispute T&M invoices?

Yes, especially when backup is thin or rates were never signed. Reduce disputes with dated time narratives, receipt files, and change orders for scope shifts. This is general business guidance, not legal advice.

Is a markup on materials allowed?

If your contract or law allows it, yes. Some buyers forbid markup and only reimburse documented cost. Others allow a stated percent for handling, warehousing, or rush procurement. Put the rule in writing before you bill.

How often should I send T&M invoices?

Weekly or biweekly is common for active jobs because it keeps totals small and gives early warning before caps are hit. Long dormant projects may bill monthly. Match the cadence to what the purchase order or master agreement requires.

Does T&M remove the need for change orders?

No. Even with T&M, clients expect notice before large scope shifts, premium overtime, or major material jumps. A light change order habit prevents surprise at approval time.

What industries use time and materials the most?

Repair trades, IT services, consulting, legal and accounting hourly matters, creative studios with open ended rounds, and construction tasks with unknown site conditions often default to T&M or T&M with a cap.

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