Why tenths, not quarters?
Law firms, accounting firms, and consulting agencies have used tenth-of-an-hour billing (0.1 hr increments) since the 1970s. Three reasons:
- Granularity. A six-minute slice fits client-facing work better than 15. A 4-minute phone call doesn’t feel like a quarter-hour, but it’s easy to round up to 0.1.
- Profitability. Always-up rounding to tenths captures more billable time than always-up rounding to quarters — specifically, you bill 6-min increments instead of 15-min increments, but you bill all of them.
- Client expectation. Decimal-tenth billing has become the professional-services convention. Clients know what 1.4 hours means; they may push back at “1.5 hours” for a job that took 1 h 25 m.
The freelance billing math
| Time spent | Tenths (round up) | Quarter (round up) | At $100/hr difference |
|---|---|---|---|
| 3 min | 0.1 (6 min) | 0.25 (15 min) | $15 |
| 7 min | 0.2 (12 min) | 0.25 (15 min) | $5 |
| 14 min | 0.3 (18 min) | 0.25 (15 min) | −$5 |
| 22 min | 0.4 (24 min) | 0.50 (30 min) | $10 |
| 30 min | 0.5 | 0.5 | $0 |
| 47 min | 0.8 (48 min) | 0.75 (45 min) | −$5 |
| 53 min | 0.9 (54 min) | 1.00 (60 min) | $10 |
Tenths-based billing produces lower per-event charges but more consistent hourly capture. Over a normal month, the totals approximately equal — with tenths slightly favoring the freelancer because there are more rounding events.
The 6-minute decimal cheat sheet
Memorize these and you can do mental conversion of any time-tracker entry to billable tenths instantly:
- 1–6 min → 0.1 hr
- 7–12 min → 0.2 hr
- 13–18 min → 0.3 hr
- 19–24 min → 0.4 hr
- 25–30 min → 0.5 hr
- 31–36 min → 0.6 hr
- 37–42 min → 0.7 hr
- 43–48 min → 0.8 hr
- 49–54 min → 0.9 hr
- 55–60 min → 1.0 hr
What to put in your engagement letter
The single most defensible billing practice is documenting the rounding rule before you start work. Sample language:
“Time will be tracked in tenth-of-an-hour increments (six minutes). Any task taking more than zero seconds and less than six minutes will be billed as 0.1 hours. Tasks longer than six minutes will be rounded up to the next 0.1-hour increment. Internal time tracking is to-the-second; invoice line items are rounded for readability.”
Two reasons this matters: clients know what they’re agreeing to (no surprise invoices), and you have a written defense if a client disputes a line item.
The minimum billable increment problem
The most contentious freelance billing question: should a 30-second email reply be billed as 0.1 hr (6 min)?
The professional services convention says yes — the minimum billable increment is 0.1, regardless of actual time spent. The client benefits from the asynchronous email; you get compensated for context-switching cost.
But applied poorly, this convention causes friction. Rules of thumb:
- Group multiple tiny tasks for the same client into one 0.1 line item. (5 emails replied to in succession = 0.1, not 0.5.)
- Don’t bill 0.1 for an email reply that says “Got it, thanks!” with no substantive thinking.
- If a client questions a 0.1 line item, write a one-line description that conveys the value (“Reviewed contract amendment Section 4.”).
The block-of-time billing alternative
Some freelancers reject decimal-hour billing entirely in favor of block-of-time pricing: $1,500 for the deliverable, period. This eliminates rounding disputes — but only works for well-scoped work. For ongoing or open-ended engagements, hourly is still the norm.
Tooling recommendations
- Toggl Track — free tier, decimal display by default, easy export to CSV.
- Harvest — integrates with invoicing; tenth-hour rounding can be configured.
- Clockify — very generous free tier; rounding rules per project.
- Manual spreadsheet — works fine for solo practitioners; use our timesheet calculator for the math.
The one number to put on every invoice line
Decimal hours, two decimal places. No HH:MM. Clients are running your invoice through their AP system, which expects decimal. Mixing formats triggers manual review and slows payment.
For agencies with junior staff who track in HH:MM, run everything through our conversion calculator before invoicing. The hour you save on data-entry friction is itself billable.
