Time tracking sounds simple until you're juggling hourly billing, decimal hours on a timesheet, daily rates for some clients and hourly for others, and a payroll system that wants everything in a different format. The arithmetic is straightforward, but the places where rounding errors and unit mismatches sneak in are surprisingly easy to miss.

Decimal Hours vs Hours and Minutes

The single most common source of confusion in time billing is the difference between "1:30" and "1.5".

On a digital clock, 1:30 means one hour and thirty minutes. In decimal hours (the format most billing and payroll software uses), 1.5 means one and a half hours — which is the same thing. But 1:30 is not the same as 1.3 decimal hours, which would be 1 hour and 18 minutes.

The conversion is:

decimal hours = hours + (minutes ÷ 60)

So 2 hours 45 minutes = 2 + (45 ÷ 60) = 2.75 decimal hours.

And going back:

minutes = decimal fraction × 60

So 3.4 hours = 3 hours and (0.4 × 60) = 3 hours 24 minutes.

This matters when you're entering time manually into an invoice or timesheet. If you track "2h 15m" on paper and enter "2.15" into your billing software, you've billed for 2 hours and 9 minutes instead of 2 hours and 15 minutes — a 6-minute shortfall. At $150/hour, that's a $15 error on a single entry. Across a month of timesheets, these small errors accumulate.

Use the time converter to check your conversions, or keep a reference table for common values:

Converting Between Hourly and Daily Rates

Freelancers and contractors often need to convert between day rates and hourly rates, either because a client requests one format or because they're comparing job offers quoted differently.

The standard workday is 8 hours, so:

day rate = hourly rate × 8
hourly rate = day rate ÷ 8

A $100/hour rate is a $800/day rate. A £600/day rate is £75/hour.

But not everyone works 8-hour days. Some creative and consulting industries use a 7-hour day (the logic being that 7 billable hours is a realistic expectation once you account for admin and breaks). If your day rate is based on 7 hours:

hourly rate = day rate ÷ 7

Always clarify with a client what they mean by "day." A £500/day engagement where the client expects 10-hour days is not the same as one expecting 7. The ambiguity is common enough that it's worth making explicit in your contract.

Billing Increments: The Rounding Question

Most billing systems round time to some minimum increment — typically 15 minutes (0.25 hours), though some use 6 minutes (0.10 hours) and others bill in full hours.

15-minute increments (0.25h): Common in professional services, legal billing, and consulting. A 22-minute call rounds to 30 minutes. A 7-minute call rounds to 15 minutes.

6-minute increments (0.10h): Standard in legal billing, where accuracy matters and rounding to 15 minutes loses significant time over the course of a day. A 7-minute call rounds to 12 minutes (0.2h). This requires more careful tracking but reduces underbilling.

1-hour minimum: Some freelancers charge a minimum of one hour per engagement, regardless of actual time. Common for consultation calls or short creative tasks where the context-switching cost is high.

Actual time: No rounding — you bill to the minute or the nearest minute. More equitable in theory, but harder to track unless you use automatic time-tracking software.

The rounding method compounds over time. If you round up to 15 minutes on every task and average 8 tasks per day, you're adding up to 2 hours of billable time per day that may or may not reflect actual work. Most clients accept standard rounding conventions; some specifically require exact time in the contract.

Payroll: Hours Per Day, Week, and Year

Payroll calculations typically require converting between hourly, daily, weekly, and annual figures. The standard US full-time equivalents:

• 1 workday = 8 hours
• 1 workweek = 40 hours (5 days × 8 hours)
• 1 work year = 52 weeks × 40 hours = 2,080 hours

To convert an annual salary to an hourly rate:

hourly rate = annual salary ÷ 2,080

A $65,000 annual salary works out to $65,000 ÷ 2,080 = $31.25/hour.

For part-time employees, adjust the denominator:

• 20 hours/week × 52 weeks = 1,040 hours/year
• 30 hours/week × 52 weeks = 1,560 hours/year

In the UK, full-time is typically 37.5 hours/week (not 40), making the annual hours figure 37.5 × 52 = 1,950 hours. This affects hourly rate calculations when comparing UK salaries to US ones.

Overtime Calculation

In the US, non-exempt employees are entitled to 1.5× their regular rate for any hours over 40 in a workweek (and in some states, over 8 in a single day).

The calculation:

regular weekly pay = hourly rate × 40
overtime pay = hourly rate × 1.5 × overtime hours
total weekly pay = regular weekly pay + overtime pay

Example: An employee earning $18/hour works 47 hours in a week.

• Regular pay: $18 × 40 = $720
• Overtime: $18 × 1.5 × 7 = $189
• Total: $909

Some employees are paid a salary for all hours worked with no overtime. Exempt vs non-exempt status under the FLSA is determined by job duties and salary level, not by employer preference — misclassifying employees to avoid overtime is a legal risk.

Time Zones in Billing for Remote Work

One practical issue that arises with international clients: whose time zone defines working hours and billable time?

A contractor in Berlin working for a client in New York may be billed at German working hours (9am–5pm CET) but the client expects some overlap with New York business hours (EST is 6 hours behind). If the contract says "8 hours per day" and the contractor's 8 hours ends at 5pm Berlin time (11am New York time), there's only 2 hours of business-hour overlap.

This isn't just a scheduling issue — it affects how time entries are timestamped in shared project management tools, and whether "end of day" means end of your day or the client's.

Clarify this upfront. Most international contracts specify which time zone defines business hours, and remote workers typically work in their own time zone unless real-time collaboration is required.

Rounding to Avoid Underbilling

A common mistake among new freelancers is consistently rounding down. "It was only 37 minutes, I'll call it 30." Done once, that's a minor concession. Done on every task across 20 clients over a year, it's thousands of dollars in lost revenue.

Rounding decisions should be symmetric: if your increment is 15 minutes, both 7-minute tasks (round down to 0) and 8-minute tasks (round up to 15) should be handled consistently. The industry norm for 15-minute billing is to round to the nearest 15 minutes — not always up, not always down.

If you want a simple consistent rule: track exact minutes, then round each entry to your billing increment at invoice time. Most billing software does this automatically once you set the increment.

Quick Reference for Common Conversions

For the arithmetic you'll do repeatedly:

• Minutes to decimal hours: divide by 60
• Decimal hours to minutes: multiply by 60
• Hourly to daily (8h day): multiply by 8
• Daily to hourly (8h day): divide by 8
• Annual salary to hourly (US, 40h week): divide by 2,080
• Hourly to annual (US, 40h week): multiply by 2,080

The time converter handles any of these conversions directly — useful when you need to double-check a calculation before sending an invoice.