Time Tracking for Agencies: How to Bill Clients Accurately

A study by Harvest found that agencies lose an average of 20–30% of billable time to poor tracking habits. That is not a rounding error — for a 5-person agency billing $150/hour, it is $180,000 a year left on the table.

The problem is rarely laziness. It is friction. When tracking time feels like a chore, people do it late, inaccurately, or not at all. The fix is a system that makes tracking faster than not tracking.

Why most agencies underbill

Three patterns cause underbilling, and they appear in nearly every agency:

• End-of-day logging. When you reconstruct your day from memory at 6pm, you typically recover 60–70% of actual time. The rest gets rounded down or forgotten.
• Unbillable creep. Quick Slack messages, revision rounds outside scope, and informal calls add up. Without tracking, they get absorbed as overhead.
• Disconnected tools. When your time tracker and invoicing tool are different apps, converting entries to invoices is a manual process — and manual processes introduce errors.

The solution to all three is the same: track time in the same system where you invoice, and make logging a one-click action, not a form.

Which billing model fits your agency

Before choosing software, choose a billing model. Each has different time tracking implications:

Hourly billing

The most transparent model — clients pay for actual time. Requires accurate, granular tracking. Best for agencies where scope is hard to estimate. Risk: unpredictable invoices can create friction.

Fixed-price projects

You quote a flat fee and absorb time overruns. You still need to track time internally — not to bill the client, but to know if the project was profitable and to price future work accurately.

Retainers

The agency gold standard. A client pays a fixed monthly fee for a set number of hours or deliverables. Time tracking tells you whether you are over- or under-delivering, and it gives you data to renegotiate rates annually. Always track time against retainers even when you do not surface it in invoices.

How to track time accurately

Accurate time tracking is a habit before it is a feature. Here is what works:

1. Log in real time, not retrospectively. Start a timer when you start a task. Stop it when you stop. Agencies that adopt timers see an immediate 15–25% increase in captured billable hours.
2. Use a timer that is always visible. If you have to open an app to start tracking, you will forget. The best time trackers live in your browser toolbar or menu bar — one click to start, one click to stop.
3. Link every entry to a project and task. Raw time entries with no context are useless for invoicing and profitability analysis. Require your team to tag every entry to a project. This takes 10 seconds and saves hours at invoice time.
4. Set a daily check-in. At the end of each day, review your time entries. This catches anything you forgot to log and lets you correct descriptions before they go stale.
5. Track non-billable time too. Admin, internal meetings, sales calls — tracking everything tells you what percentage of your hours are actually billable. A healthy agency targets 65–75% billable utilisation. If you are below 50%, you have a capacity problem.

Turning time entries into invoices

This is where most agencies lose money. The disconnect between tracking and invoicing means entries get reviewed manually, some get missed, and the process takes hours every billing cycle.

The right workflow:

1. Track time entries against client projects throughout the month.
2. At billing time, pull all unbilled entries for the project.
3. Review for accuracy — descriptions, durations, billable flags.
4. Generate an invoice with one click that includes the line items, grouped by task or date.
5. Send to the client with a payment link.

With OnBrio's time tracking, steps 3–5 take under two minutes. Unbilled hours surface automatically as a banner on your dashboard. You click “Generate Invoice,” review the entries, and send — all without leaving the platform or opening a second tool.

Handling client disputes

Time billing disputes usually come down to one thing: the client does not believe the hours reflect the work delivered. The fix is transparency, not justification.

• Detailed entry descriptions. “Design work” is not a line item. “Designed responsive header component + 2 revision rounds per brief” is.
• Weekly or bi-weekly time reports. Share a summary of hours spent before the invoice arrives. No one is surprised at billing time.
• Milestone-based billing for fixed projects. Invoice at deliverable completion, not at month end. Ties payment to tangible output.
• Scope change documentation. When work falls outside the original scope, log it with a note and flag it before completing — not after invoicing.

Best time tracking software for agencies

There are dozens of time tracking tools. Here is how the main options compare:

• Toggl Track. Best standalone timer. Clean UI, excellent browser extension. No native invoicing, no client portal. You still need 3–4 other tools.
• Harvest. Time tracking + basic invoicing. Better integration than Toggl but limited project management and no client portal.
• Clockify. Free for unlimited users. Good for budget-conscious teams but lacks agency-specific features like proposals, contracts, and client portals.
• OnBrio. Time tracking built into the same platform as proposals, contracts, invoicing, client portals, and project management. Track time → generate invoice → send to client → collect payment, all in one place.

If you are running an agency, a tool that connects time tracking directly to invoicing saves 3–5 hours per billing cycle. Multiply that by 12 months and you recover weeks of capacity per year.

See how OnBrio handles time tracking →

Common questions