Most consultants don't go looking for "time tracking software" and "invoicing software" separately — they end up with both anyway, stitched together with exports and copy-pasting. The actual question isn't which timer app has the nicest interface. It's whether the hours you log ever have to be typed into an invoice by hand, because that re-entry step is where errors, delays, and forgotten hours all happen.
The only feature that matters: does logged time become an invoice line item on its own?
A timer that just produces a CSV isn't billing software — it's tracking software with an export button. The distinction shows up the moment you go to invoice: if you're opening a spreadsheet, filtering by client, and manually typing totals into a separate invoicing tool, you've bought two products that don't actually talk to each other. What you want is a system where a logged entry — client, task, hours, rate — is already an invoice line item waiting to be sent, not raw data waiting to be transcribed.
Two-tool setup:You track 14.5 hours across three clients in a timer app this week. Friday, you export a CSV, sort it by client, and manually build three invoices in a separate tool — re-typing each line, double-checking the math, and hoping you didn't drop an entry logged from your phone on Tuesday.
Tied-together setup:The same 14.5 hours are already sitting on three draft invoices, grouped by client, at each client's rate. You review the line items, confirm nothing looks off, and send. Ten minutes instead of an hour, and no entry gets lost between systems.
Retainer allotments and overage need to be automatic, not a mental note
If any part of your practice runs on retainers, plain time tracking breaks down fast. A generic timer just adds up hours — it has no concept of "this client gets 20 hours included, and anything past that bills at the overage rate." That math is left to you, every month, which is exactly the kind of manual step where a client quietly gets under-billed for a few hours you forgot to flag.
A client's retainer includes 20 hours a month at a blended rate of $150/hr ($3,000 flat), with overage at $200/hr. This month you logged 24.5 hours against them. Software that understands retainers bills the flat $3,000 for the first 20 hours and automatically adds 4.5 hours × $200 = $900 as a separate overage line — $3,900 total, with the split visible on the invoice. Software that only tracks time gives you "24.5 hours logged" and leaves the $3,000-vs-overage math, and the risk of getting it wrong, entirely on you.
Look specifically for a tool that lets you set a monthly hour allotment per client or per retainer, then handles the split automatically when you go over. If a vendor can't describe how overage billing works in a demo, assume it doesn't exist as a real feature.
It has to stay clean across multiple clients, not just one
A lot of time-tracking tools are built around a single ongoing project, which is fine for an employee but wrong for a consultant juggling five or six clients at different rates and different billing arrangements. The test isn't whether the tool can track multiple clients in theory — it's whether switching between them during a working day is fast enough that you'll actually do it in real time, instead of reconstructing your week from memory on Friday afternoon.
- Per-client rates:your $200/hr retainer client and your $150/hr project client shouldn't require a workaround to bill correctly from the same timer.
- Fast client switching:if starting a new entry takes more than a couple of taps, you'll stop logging time as you go and start guessing later.
- Client-level invoice history:you should be able to see, per client, what's been billed and what's still sitting in unbilled hours — without cross-referencing two tools.
Ask what happens at the moment you hit "send invoice," not before
Most demos focus on how easy the timer is to start. That's the least important part. What actually determines whether the tool saves you time is what happens next: does it turn a week of entries into a reviewable draft invoice with correct rates and retainer math already applied, or does it hand you a number you still have to build an invoice around? If you're evaluating options, ask to see that exact transition — logged hours to sendable invoice — before you commit.
Once billing is tied directly to logged time, the free Consulting Invoice Generatoris a fast way to see what a clean, correctly itemized invoice should actually look like, even before you've settled on a full time-tracking system.