Time-tracking & billing, in plain English

Utilization rate is the share of a person's or team's available working hours spent on billable, revenue-generating work, calculated as billable hours divided by available hours (after PTO and holidays) times 100.

For most professional services firms, a healthy billable utilization rate sits between 74% and 85%: below it, margins erode from idle paid capacity; above it, burnout, quality problems, and inflated timesheets become likely. The right target varies by role — junior staff typically run higher (78%–88%) than senior consultants and partners, who spend more time on business development. Utilization is often confused with capacity utilization or realization rate, but each measures something different: utilization diagnoses staffing, not revenue conversion.

Realization rate is the percentage of recorded billable hours that actually gets invoiced and collected, exposing revenue lost to write-offs, write-downs, and collection shortfalls that utilization alone never shows.

Realization erodes in two stages: at billing review (vague descriptions, budget caps, or discretionary write-offs) and at collection (disputes, late payments, bad debt). Most professional services benchmarks put a healthy combined realization rate at 85%–95%; rates below 80% typically signal a systemic capture or billing-review problem, not a capacity issue. A firm can be highly utilized yet have poor realization if it writes off hours before they reach an invoice, which is why both metrics need to be tracked together.

Project margin is the profit a services engagement earns after its delivery cost, calculated as (revenue − cost) ÷ revenue × 100, using each person's loaded cost rate against the hours they logged.

Gross (delivery) margin counts only direct labor cost and tells you whether a project itself is profitable; net margin subtracts firm-wide overhead too, and tells you whether the whole business is. Industry benchmarks put a healthy gross margin above 50% and net margin at 15%–30%. Margin erodes quietly through scope creep, over-servicing, and putting expensive seniors on work juniors could handle, which is why it needs to be measured per project and per client continuously, not just at quarterly close.

Effective (blended) hourly rate is the revenue a firm actually collects divided by the total hours worked — almost always lower than the stated bill rate because of write-offs, discounts, and fixed-fee overruns.

The gap between the stated bill rate and the effective rate — the rate realization gap — is one of the clearest signals of where pricing and billing are quietly losing value. A $200/hour bill rate that realizes only $158/hour, for example, means the firm is capturing just 79% of its pricing power. Tracking effective rate at the project, client, and firm level, alongside utilization and realization, shows exactly what each hour actually earns, not just what it's billed at.

Cost rate is the fully loaded cost to a firm of one hour of a person's time — salary plus taxes, benefits, and an allocated share of overhead, divided by their realistic billable hours.

Dividing salary by 2,080 calendar working hours dramatically understates cost, because it ignores payroll taxes and benefits (often 27%–45% of salary combined), firm overhead, and — the number most firms miss — that a person's realistic billable hours are always fewer than their total working hours. The margin on every hour logged is simply bill rate minus cost rate, and cost rate is typically 1.5x–2.5x someone's raw salary-based hourly rate, which sets the pricing floor below which every billed hour loses money.

Bill rate is the hourly amount a firm charges a client for someone's time on an engagement — the number that appears on invoices, in contracts, and in project estimates.

The margin on any hour is the gap between bill rate and cost rate: bill $150 and cost $90, and the firm earns $60 an hour before write-offs reduce what's actually collected. Bill rates should be set above the cost-rate floor by the firm's target margin, then checked against what the market for that role, service, and geography will actually bear — most firms use role-based rates (a standard rate per level) rather than quoting a rate per individual.

Time & Materials (T&M) is a billing model where a client pays for actual hours worked at an agreed rate, plus reimbursable expenses — so revenue scales directly with effort and scope risk sits with the client.

T&M is the safer model for complex or uncertain work, since scope changes simply generate more billable hours rather than eating into a fixed fee — but it leaves the client uncertain about the final invoice total. A common middle ground is T&M with a not-to-exceed (NTE) cap, which limits the client's cost while still letting the firm bill actual time up to that ceiling.

Fixed Price (or Fixed Fee) is a billing model where a client pays one set amount for a defined deliverable, no matter how many hours it actually takes — so scope risk sits with the firm, not the client.

Fixed Price lets a firm keep the upside if it delivers faster than estimated, but every hour beyond the estimate comes straight out of margin — which is why scope creep and estimation error are the model's two biggest risks. It works best when scope is precisely defined, the work is repeatable, and the firm has reliable historical data and disciplined change-order practices.

Billable hours are the hours a services firm can charge a client for under its agreement — delivery work, client meetings, and in-scope research or revisions.

The simplest test is a question: would this client reasonably expect to see this time on their invoice? Billable time is the only category that directly produces revenue, and it feeds every other core metric — you can't calculate utilization, realization, or margin without a clean, consistent billable/non-billable split, tagged at the point of entry rather than reconstructed from memory at week's end.

Non-billable hours are legitimate work a services firm performs that no client pays for directly — internal meetings, admin, training, business development, and overhead.

Non-billable time isn't waste — it's the cost of running and growing a firm, and it has to be funded out of the margin billable work produces. The goal isn't to eliminate it but to keep it intentional and measured; problems start only when it quietly grows, drags utilization below target, and erodes margin without anyone noticing.

A write-off is billable time a firm worked and paid salary for, then removes from an invoice before the client ever sees it — the most invisible profit leak in professional services.

The typical services firm writes off 5%–15% of its recorded billable hours, most often because of vague time descriptions, budget caps hit with no change order in place, or discretionary cuts at billing review. Most practitioners aim to keep write-offs under 5%–8% of billable hours; the goal isn't zero write-offs but intentional ones — chosen and measured, not accidental erosion month after month.

The monthly billing close is the structured process a services firm runs at the end of each period — locking timesheets, reviewing and approving billable entries, and generating invoices — to convert a month of logged hours into revenue without losing any of it.

Done well, it runs five stages — a mid-month sweep, a final-entry reminder, a timesheet lock, billing review, and invoice generation — and takes just 1–2 days for a firm with good daily time-capture discipline. Most services firms lose more revenue in this process than to any other single cause, almost entirely through late submissions, vague descriptions, and budget overruns with no change order in place.

An MCP (Model Context Protocol) server is a standard endpoint that lets any MCP-capable AI assistant — Claude, Cursor, or a custom agent — connect directly to a company's time-tracking data and act on it, without exports or custom API glue code.

Introduced by Anthropic, MCP works like “USB-C for AI”: a tool exposes one MCP server and any MCP-capable client can discover and call its tools. Timix.AI exposes its MCP server at api.timix.ai/api/integration/v1/mcp, governed per API key — sensitive data like cost rates and profit margins stays redacted by default, and every write the AI makes is created as a draft, scoped to that key's role.

Overhead (OVH) is a third billing type — alongside Time & Materials and Fixed Price — for internal or administrative work that doesn't attach to any client project, and is non-billable by definition.

Tracking OVH time separately matters because it flows into utilization calculations and true cost allocation — lumping internal work into T&M or fixed-fee projects distorts both project margin and a team's real billable capacity. Tagging every task with its billing type (T&M, Fixed Price, or OVH) lets each logged hour roll up automatically into the right bucket.

A retainer is a recurring fee a client pays a services firm — usually monthly — for an agreed bucket of hours or ongoing availability, rather than being billed project by project.

Retainers give clients budget predictability and firms recurring revenue, but they fail quietly rather than loudly: a team can over-service a retainer client month after month without realizing the extra hours are simply absorbed, unbilled work. Watching retainer burn against the agreed hour bucket in real time — the same discipline used for capped Time & Materials work — is what keeps a retainer profitable instead of a slow margin leak.

Capacity is the total working time a person or team has available in a period — the denominator behind utilization rate, and one that must reflect real work schedules and holidays rather than a flat calendar figure.

Using a flat denominator — like 2,080 hours a year — ignores that people work different schedules, take different holidays by country, and use PTO, which structurally distorts capacity and penalizes people for taking earned time off. Per-user work schedules and per-region holiday calendars are what let capacity, and the utilization rate built on top of it, reflect who actually worked when.

A Statement of Work (SOW) is a contract document that defines the scope, deliverables, timeline, and pricing of a client engagement — the reference every hour billed and every change request is measured against.

The SOW is what turns a vague agreement into an enforceable scope: it states exactly what the firm will deliver, by when, for how much, and under which billing model — Time & Materials, Fixed Price, or milestone-based. A precise SOW is the firm's main defense against scope creep, because any work beyond it is grounds for a change order rather than an unbilled favor. On fixed-fee engagements especially, the sharper the SOW, the easier it is to protect margin when the client asks for “just one more thing.”

Work in Progress (WIP) is billable work a firm has already performed but not yet invoiced — hours that are earned and sitting on the books, waiting to be converted into an invoice.

WIP is the pool of value between doing the work and collecting for it, and the longer hours sit there unbilled, the higher the risk they turn into write-offs or are forgotten entirely. Watching WIP aging — how long recorded time waits before it reaches an invoice — is one of the clearest early warnings of revenue that is slipping away. A disciplined monthly billing close exists largely to clear WIP promptly, while descriptions are fresh and clients still expect the charge.

A blended rate is a single average hourly rate charged across a team of mixed seniority, instead of billing each person at their own individual rate.

Firms use a blended rate to simplify pricing and proposals: rather than quoting a partner rate, a senior rate, and a junior rate separately, the client sees one number for the whole team. Its profitability depends entirely on the actual staffing mix — if more senior time is spent than the blend assumed, margin quietly erodes, so the planned mix has to hold in practice. This is distinct from the effective blended hourly rate, which measures what a firm actually earns per hour after write-offs and discounts, rather than the rate it quotes up front.

Scope creep is the gradual expansion of a project's work beyond what was agreed, where small additions accumulate until the effort no longer matches the price — quietly eroding margin, most sharply on fixed-fee work.

Each individual request feels too small to charge for — a quick revision, one more report, a slightly wider brief — but together they consume hours the price never accounted for. On Fixed Price engagements scope creep comes straight out of margin, since the fee is capped while the effort is not; on Time & Materials it is less dangerous because extra work simply bills as extra hours. The defense is a precise Statement of Work plus a disciplined change-order process, so expanded scope triggers a conversation about price rather than a silent write-off.

Revenue leakage is billable work that a firm performs but never invoices, so revenue it genuinely earned quietly goes uncollected and disappears from the books.

Leakage happens at the seams of the billing process: time that never gets logged, hours that sit as WIP until everyone forgets them, entries written off at review, or invoices that go out under-scoped. Unlike a discount, it is rarely a decision — it is earned revenue slipping away by default, and industry studies routinely put it at 5%–15% of potential fees. Closing the gaps means capturing time at the point of work, aging WIP visibly, and running a tight monthly billing close so nothing earned goes unbilled.

Budget burn rate is the pace at which a project consumes its hour or fee budget over time — how fast the budget is being spent relative to how much work remains.

Comparing burn rate to project progress is what tells you whether an engagement is on track: burning 70% of the budget at the halfway mark is an early signal that the project will overrun and margin is at risk. Watching burn in real time — rather than discovering the overrun at closing — is what lets a firm act while options still exist, whether that means a change order, re-staffing to cheaper roles, or resetting client expectations. On fixed-fee work the burn rate is effectively a margin countdown, since every hour past budget comes straight out of profit.

Milestone billing is invoicing a client when defined project milestones are completed — a set payment per deliverable or phase — rather than billing by the hour or in equal monthly installments.

Milestone billing ties cash flow to visible progress, which reassures clients on larger fixed-fee engagements and protects the firm from delivering months of work before seeing any payment. It depends on a precise Statement of Work: each milestone needs a clear, acceptance-ready definition, or “done” becomes a dispute that delays the invoice. Firms typically pair it with an upfront deposit and track hours against each milestone's fee, so an overrun on an early phase doesn't silently consume the margin budgeted for later ones.

Accrued (unbilled) revenue is earned but not-yet-invoiced work, recognized as revenue in the period it was performed rather than in the later period when the invoice is actually issued.

Accrual accounting matches revenue to the period in which the work happened, so a firm's financials reflect what it actually earned that month even when billing lags behind. It is the accounting counterpart to WIP: the hours sitting unbilled on the books are recognized as accrued revenue until an invoice converts them into a receivable. Getting the accrual right depends on complete, timely time capture — hours never logged can't be accrued, which is one more way sloppy time tracking understates a firm's real performance.

Timesheet approval is the review step where a manager verifies a person's logged hours — checking they are accurate, complete, and correctly marked billable or non-billable — before the time is billed or the period is locked.

Approval is the last quality gate before hours turn into invoices, and it's where vague descriptions, miscategorized time, and missing entries get caught while they're still cheap to fix. Once a timesheet is approved and the period is locked, the numbers feed billing, utilization, and margin, so a rushed or skipped approval propagates errors straight into client invoices and management reports. A clean approval step is a core part of the monthly billing close and one of the simplest defenses against revenue that would otherwise be written off or never billed.

Chargeability is the share of a person's paid working time that is billable to clients — closely related to utilization, and often used interchangeably with it in accounting and consulting firms.

In practice chargeability and utilization measure the same thing — billable time as a proportion of available time — with “chargeability” being the term of choice in many audit, tax, and consulting practices. Where firms differ is the denominator: some measure against total paid hours, others against a target capacity net of PTO and holidays, and the two can produce meaningfully different percentages for the same person. Whichever convention a firm adopts, it needs to apply it consistently, because chargeability targets drive staffing decisions, bonuses, and each person's contribution to margin.

Net payment terms are the number of days a client has to pay an invoice after it is issued — “Net 30,” for example, means payment is due 30 days from the invoice date.

Payment terms determine the gap between doing billable work and actually collecting for it, and longer terms — Net 30, Net 60, or worse — tie up cash the firm has already paid out in salaries. They're a lever, not a fixed cost: shortening terms, invoicing promptly at the monthly close, and enforcing due dates all pull cash in faster and reduce the working capital a firm has to carry. Terms only help if invoices actually go out on time, which is why disciplined billing and clear terms work as a pair.

Cost-plus pricing is setting a client price by taking the cost of delivering the work and adding a fixed markup — so the fee is driven by cost rate rather than by the value delivered or the market rate.

Cost-plus is simple and easy to justify — a 40% markup on a $100/hour cost rate yields a $140 bill rate — but it anchors pricing to internal cost instead of the value a client actually receives, which usually leaves money on the table. Its whole integrity rests on an accurate, fully loaded cost rate: a markup applied to an understated cost (one that ignores payroll taxes, benefits, and overhead) can produce a bill rate that looks profitable yet loses money on every hour. Most mature firms treat cost-plus as a floor for what they must charge, then price up toward what the market and the value delivered will bear.

Time and Expense (T&E) is billing a client for both the hours worked and the reimbursable expenses incurred on their behalf — travel, software, subcontractors — passed through on the same invoice.

T&E is the expense side of a Time & Materials engagement: alongside billable hours, the firm passes through costs it laid out for the client, sometimes at cost and sometimes with an agreed handling markup. Capturing these expenses against the right project matters as much as capturing time — an unlogged flight or software license is money the firm paid that the client never reimburses, a direct hit to project margin. Clear rules in the Statement of Work about which expenses are billable, and at what markup, prevent disputes when the invoice arrives.

A client engagement is a defined body of contracted work a firm performs for a client — the unit around which time, budgets, billing, and profitability are organized.

An engagement is the level at which most professional services firms actually manage the business: a Statement of Work defines it, a budget bounds it, hours are logged against it, and its margin is measured on its own. One client may run several concurrent engagements — a fixed-fee project, an ongoing retainer, a Time & Materials advisory — each with its own scope, billing model, and profitability. Tracking at the engagement level is what lets a firm see which specific pieces of work make money and which quietly lose it, rather than only knowing whether the client overall is profitable.