How to calculate hours worked, overtime and time bank without errors (8h30 is not 8.3 hours)

By Marcelo Amantino · published October 21, 2026 · 3 min read · who we are

At the end of the month you add up the hours, the total does not match the one from HR and nobody knows who got it wrong. For freelancers, the math decides how much to charge. For employees, it decides whether the time bank is right. And the most common mistake is a silly one: treating 8h30 as if it were 8.30. Let us get to the method and to the places where the math usually slips.

The mistake that breaks the sum: 8h30 is not 8.30

An hour has 60 minutes, not 100. So 8h30 is worth 8.5 hours, not 8.3. Anyone who adds up times as if they were decimal numbers loses minutes without noticing. To convert hours and minutes to decimal, divide the minutes by 60: 8h45 is 8 + 45/60 = 8.75. That decimal value is what you multiply by the hourly rate to bill a client.

How to calculate a working day

The math is: end time minus start time, minus breaks. Example: you started at 8:00, left for lunch at 12:00, came back at 13:00 and went home at 17:30. From start to finish that is 9h30; subtracting 1 hour for lunch, the total for the day is 8h30. If your daily workload is 8h, the day’s balance is +0h30. At the end of the month, the balance is the sum of the daily balances.

Step by step in the Hours Calculator

Open the Hours Calculator.
Enter the start, the end and the break for each day, and the daily reference workload.
See the total worked, the day’s balance and the month’s totals.
At closing time, export the CSV to open in Excel or Google Sheets or to hand to HR.

Shifts that cross midnight

People who work at night face the classic: starting at 10 pm and ending at 6 am would give a negative result if the system did not know the end is the next day. The calculator indicates when a shift goes past midnight (it shows as “+1 day”), but always check the result of a night shift before relying on it.

Overtime: what the calculator does and what it doesn’t

The calculator adds up the hours and compares them with the workload, showing whether there are extra hours or hours to make up. It does not calculate the value of the overtime premium, because that depends on your contract and your collective agreement. As a general rule, in Brazil the Constitution provides that overtime be paid with a premium of at least 50% over the normal hourly rate, but your case may have its own rules, including time bank rules. Check your contract and your category’s collective agreement, or ask HR.

For freelancers: from time to value

Add up the month’s hours, convert to decimal and multiply by the hourly rate. Record the time on the same day you worked: rebuilding the day from memory at the end of the month is the main source of errors, and of arguments with the client. If the client demands a report, the calculator’s CSV is a good starting point.

Limits worth knowing

It is a support calculator, not a replacement for the company’s official time clock.
Records are saved only in this browser, on this device: clearing the site’s data erases the history, and they do not sync between devices. Export the CSV regularly to keep a copy.
Nothing is sent to WebFaz: there is no account and no server.