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DevTools / 勤務時間計算・タイムシート

勤務時間計算・タイムシート

Adding up a timesheet by hand is where arithmetic errors become payroll disputes. This calculator takes start and end times row by row, subtracts unpaid breaks, handles shifts that cross midnight without producing a negative duration, rounds to whatever increment your payroll uses, and totals the result in hours and minutes, in decimal hours and in minutes, with a configurable overtime threshold and pay rate. The whole sheet exports as CSV for a payroll system or a client invoice.

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LabelStartEndBreak (min)SpanWorkedDecimal
8h 30m8h 00m8.000
9h 15m8h 30m8.500
8h 00m+1d7h 30m7.500
Total worked
24h 00m
Decimal hours
24.000h
Total minutes
1440min
Gross span
25h 45m
Unpaid breaks
1h 45m
Regular time
24h 00m
Overtime
0h 00m
> 40h
Overnight shifts
1
An end time earlier than the start time is treated as a shift that crosses midnight, so 22:00 → 06:00 counts as eight hours.

仕組み

Time arithmetic is not decimal arithmetic, and mixing them is the source of most timesheet errors. An hour has sixty minutes, so 1 hour 45 minutes is 1.75 hours in decimal, not 1.45. Payroll systems vary in which they want: hourly rates multiply against decimal hours, while scheduling and compliance rules are usually expressed in hours and minutes. The calculator reports both, along with the raw minute total, so a figure can be entered into any downstream system without converting it by hand — a conversion that goes wrong often enough to be worth eliminating.

An overnight shift is the classic edge case. A shift starting at 22:00 and ending at 06:00 gives a negative difference under naive subtraction. The fix is to detect that the end time is earlier than the start time and add twenty-four hours, which yields the correct eight-hour duration. The subtlety is that this is a heuristic: it assumes no single shift exceeds twenty-four hours, which is true for every real employment context and false for a mis-keyed entry, so the calculator flags the situation rather than silently adjusting it.

Rounding is where policy meets arithmetic and where the two most common methods differ. Rounding each punch to the nearest increment and then subtracting — the method most time clocks use — can produce a total that differs from rounding the total duration. Rounding a 7-minute-late arrival down to the quarter hour is generous to the employer, and the practice is regulated in some jurisdictions: the United States Fair Labor Standards Act, for instance, permits rounding to the nearest five minutes or a quarter hour provided it does not systematically favour the employer over time. The calculator applies the rounding per row and states which method it used.

Overtime is a threshold applied to the total rather than to each row, because the qualifying period is normally a day or a week and the rows are just its parts. The calculator applies a configurable threshold, splits the total into regular and overtime hours, and prices each at its own rate, with overtime defaulting to 1.5 times the base as the common convention. Whether a particular threshold and multiplier is lawful depends on the jurisdiction and on the employment contract, which is why both are inputs rather than fixed assumptions.

主な利用シーン

  • Total a week of timesheet rows and export them as CSV for payroll.
  • Work out the hours between two clock times for a shift, excluding an unpaid lunch break.
  • Calculate an overnight shift that crosses midnight without a negative result.
  • Convert a timesheet into decimal hours for an invoice or a billing system.
  • Split a week into regular and overtime hours at a forty-hour threshold.
  • Check that a set of logged hours matches the total on a payslip.

最終更新: 2026-10-14 — 本文は英語で表示されます（UI は翻訳済み）。

よくある質問

How do I calculate hours worked between two times?

Subtract the start time from the end time and deduct any unpaid break. If the end time is earlier than the start time, the shift crossed midnight and the result needs a day added, which is why a naive subtraction reports a negative number for a night shift. The calculator handles that, converts the result to both hours-and-minutes and decimal hours, and sums across as many rows as you need — which matters, because the interesting errors in timesheet arithmetic happen at the boundaries between rows.

What is 7 hours 45 minutes in decimal hours?

7.75 hours. Convert the minutes by dividing by sixty — 45 divided by 60 is 0.75 — and add the whole hours. The common mistake is reading 7 hours 45 minutes as 7.45, which is a difference of eighteen minutes, or about four percent, and four percent of a payroll is a real amount of money. Use the decimal figure for any multiplication by an hourly rate, and the hours-and-minutes figure for anything a human will read.

Should breaks be deducted?

Only if they are unpaid, and that is a matter of policy and, in many places, of law. A short rest break is frequently paid while a meal break is not, and the threshold between them varies — twenty minutes is a common dividing line in the United States, and the European Working Time Directive treats a rest break after six hours differently again. The calculator takes the break as an explicit per-row input rather than assuming a default, so the policy decision stays where it belongs.

How does rounding work?

Each row is rounded independently to the increment you select — one, five, six, fifteen or thirty minutes — and the rounded values are then summed. This matches how physical time clocks and most payroll systems behave, and it is why a week of rounded days can differ from the same week rounded in total. The direction of rounding is a legal question rather than a mathematical one in several jurisdictions, so the calculator applies the nearest increment and leaves the policy decision, and its compliance, to you.

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