Create a client and a project for each job, then run a timer or enter hours as you work, tagged to that project and marked billable or not. Review the week's entries, fix gaps, and run a report per client. Use that report as the backing for your invoice, so the hours you bill match the hours you logged.
Client time slips away in two places: the hours you never logged, and the hours you logged against nothing in particular. Both end up as work you can't bill. The fix isn't a cleverer app, it's a routine that starts before the first timer runs and ends after the invoice goes out.
Below is that routine, step by step, with the trackers that handle each stage. Then there's a side-by-side table so you can see which tool covers what.
The routine, from first timer to locked invoice
Step 1: Create the client and the project before you start the clock
Time logged without a client attached is the hardest to bill later. Set up the client, then a project or task for each job. Most trackers organise work this way, and Harvest keeps clients, projects and tasks in one hierarchy.
Step 2: Log as you work, with a timer or a timesheet
Start a timer while you work, or fill in a daily or weekly timesheet at the end of the day. Logging as you go is more accurate than rebuilding the week from memory on a Friday afternoon. Every tool in the table below offers one or both, and Clockify adds calendar, kiosk and auto tracker modes on top.
Step 3: Mark each entry billable or not, and set a rate or a limit
This separates the hours you can invoice from admin time and shows when a project is running over. Everhour lets you set project limits with alerts, so you hear about an overrun while there's still time to talk to the client about it.
Step 4: Review the week and submit it for approval
Fix gaps and duplicate entries before anything reaches an invoice. Catching errors here avoids disputes later. Several of the trackers below describe timesheet approval, and TimeCamp ties it to entry locking, which matters if you've got a team logging hours on your behalf.
Step 5: Run a report for each client
Pull hours by project and task for each client. That report is the evidence behind your invoice, and it shows the client exactly where the time went. Toggl Track's reports include estimated versus actual time on every project, which is useful when you quoted a fixed scope.
Step 6: Build the invoice from the tracked hours
Create the invoice straight from the log, or export the data to your accounting tool, so the invoice and the timesheet stay identical. Most of the tools in the table below describe invoicing from tracked time.
Step 7: Lock the hours you've invoiced
Once the invoice has gone, freeze those entries. The next section explains why this step matters more than it looks.
Hours you've already billed can still change
Here's the trap. In most trackers, time you've already invoiced can still be edited unless you lock it. Someone tidies up an entry, a timer gets nudged, and suddenly your records don't match what the client was billed. If the client ever queries an invoice, that mismatch is the last thing you want.
Kimai's product page states that exported timesheet records can be locked and protected against further changes, and TimeCamp's page describes entry locking as part of its approval workflow. Whichever tool you use, check whether it can lock approved or invoiced time, and make locking the final step of every billing cycle.
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While you're checking settings, think about monitoring too, because trackers differ a lot here. Hubstaff's page lists screenshots and activity tracking, while Toggl's page states there are no screenshots. Neither approach is wrong, but clients and contractors notice which one you've picked, so choose the one that fits how you want to work with people.
Six trackers side by side
| Tool | What it does | Stands out for |
|---|---|---|
| Toggl Track | Timer, timesheet reports and invoicing, with recurring projects for retainer clients | Billable rates, revenue and profitability reports; states it takes no screenshots |
| Harvest | Daily or weekly time views, calendar-based logging, approval and invoices from tracked hours | Billable data you can export to accounting tools |
| Clockify | Timer, weekly timesheet, calendar, kiosk and auto tracker, with rates, approval, invoicing and expenses | A wide set of timekeeping modes in one tool |
| Everhour | Timers inside project tools, project limits, estimate-versus-actual reports and client invoices | Alerts when a project is at risk of running over |
| TimeCamp | Automated and AI-assisted tracking with billable hours reports and approval workflows | Entry locking to stop approved time changing |
| Kimai | Self-hosted tracking with invoice templates and exports to XLSX, PDF, CSV and HTML | Describes itself as 100% open source (AGPL 3), with lockable exported records |
Only one tracker here describes itself as open source and self-hosted, with a cloud option too. Free plan details for the others aren't spelt out on their pages, so check each one before you commit. For a broader comparison, see our roundup of time trackers for freelancers, or the list of free time tracking apps if you're just starting out.
My verdict for freelancers and small agencies
Don't spend a week choosing a tracker. Pick one that can tie every entry to a client, report per client and lock invoiced hours, then follow the seven steps every week without fail. A plain routine you stick to beats a clever app you only open when an invoice is due, and locking billed time is the habit that saves you when a client asks questions.
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Frequently asked questions
What is the best way to track billable hours for clients?
Set up a client and project, run a timer as you work, mark entries billable, then report by client before invoicing.
Can I turn tracked time into an invoice?
Yes. Harvest, Clockify and Everhour each describe invoicing from tracked time.
Is there a free or open-source time tracker?
Kimai describes itself as fully open source and self-hosted. Free plan details for the other tools here aren't stated on their pages.
Should I track time with timers or timesheets?
Either works. Timers are more accurate, while a daily or weekly timesheet suits people who'd rather log hours in one go. Most of these tools offer both.
How do I stop clients disputing my hours?
Review entries weekly, keep notes on each entry, send a report per client, and lock invoiced entries so they can't change.
