The complete guide to time cards, work hours, and overtime pay
A time card is the foundation of every payroll. Whether it is a paper sheet pinned next to the punch clock, a spreadsheet, or an app like ShiftTally, its job is the same: record exactly when each employee started and stopped working, subtract unpaid breaks, and turn those raw times into paid hours that payroll can trust. Get the math wrong and you underpay people — which destroys morale and can create legal liability — or overpay them, which quietly bleeds the business every single pay period. A reliable time card calculator removes the guesswork by converting clock-in and clock-out times into clean decimal hours, applying the right overtime rule automatically, and producing a gross pay estimate you can hand to payroll with confidence.
How work hours are calculated from clock times
The core formula is simple: paid hours = (clock-out time − clock-in time) − unpaid break minutes. A shift from 9:00 AM to 5:30 PM spans 8.5 hours; subtract a 30-minute lunch and you have 8.0 paid hours. Most payroll systems want that answer in decimal hours (8.50) rather than hours and minutes (8:30), because decimals multiply cleanly against an hourly rate. This is the number-one source of manual errors: people read 8:45 as 8.45 hours when it is really 8.75 hours, and that 0.30-hour mistake repeats every day. A dedicated work hours calculator does the conversion for you, so 7 hours 30 minutes always becomes 7.50, never 7.30.
Breaks need care. Lunch breaks are usually unpaid, so they come off the total — this is what people mean when they search for a time card calculator with lunch. Short rest breaks, typically 10 to 20 minutes, are paid working time in many jurisdictions and should not be deducted. Overnight shifts add another wrinkle: a night shift from 10:00 PM to 6:00 AM crosses midnight, so the clock-out time is numerically earlier than the clock-in time. The correct handling is to treat the clock-out as belonging to the next day, adding 24 hours before subtracting. ShiftTally detects this automatically and marks the day as overnight, so night-shift workers never have to do midnight arithmetic in their heads.
Weekly vs daily overtime: which rule applies to you?
Overtime rules decide which hours earn the 1.5× premium, and the answer changes everything. Under the US federal Fair Labor Standards Act (FLSA), the standard is a weekly threshold: hours beyond 40 in a single workweek are paid at time-and-a-half. If you work four 10-hour days (40 hours total), no overtime is owed under federal law — even though each day exceeded 8 hours. Many states and many company policies instead use a daily threshold: any hours beyond 8 in a single day earn overtime, regardless of the weekly total. With a daily rule, those same four 10-hour days produce 8 overtime hours. That is a 20% pay difference for identical work, which is why an overtime calculator that lets you switch rules is so valuable: you can see exactly what each interpretation costs.
The distinction matters for scheduling too. Under a weekly rule, a manager can compress schedules into longer days without triggering overtime, as long as the week stays at 40. Under a daily rule, every long day costs extra, which pushes schedules toward even 8-hour days. Neither is universally better — it depends on the business — but everyone involved should be able to compute both. ShiftTally keeps all three of the most common rule sets one click away, so a supervisor in Texas, a nurse in Alaska (which uses daily overtime), and a warehouse team in California can each get the right answer from the same tool.
California overtime and double time, explained
California has the most employee-friendly overtime rules in the United States, with three layers. First, the daily layer: hours 8 through 12 in a single day are paid at 1.5×, and hours beyond 12 are paid at 2× (double time). Second, the weekly layer: hours beyond 40 in the week that have not already been counted as daily overtime are paid at 1.5×. Third, the seventh consecutive day layer: on the seventh straight day of work in a workweek, the first 8 hours are paid at 1.5× and anything beyond 8 at 2×. A 13-hour shift in California therefore splits into 8 regular hours, 4 overtime hours, and 1 double-time hour — a split that is genuinely hard to do by hand across a whole team, and exactly the kind of math ShiftTally's California mode automates.
Double time is not unique to California — some union contracts and company policies use it too — but California is the biggest jurisdiction that mandates it by statute. If you manage hourly workers there, a weekly hours calculator without double-time support is simply incomplete. The same logic applies anywhere a premium tier exists: once you define the thresholds (8 hours, 12 hours, 40 hours), the rest is mechanical, and mechanical work is what calculators are for.
From hours to gross pay: the payroll math
Gross pay is pay before taxes, benefits, and other deductions. The formula follows directly from the hour buckets: gross pay = (regular hours × rate) + (overtime hours × rate × 1.5) + (double-time hours × rate × 2). Take an employee at $18 per hour who works 45 hours under a weekly rule: 40 × $18 = $720, plus 5 × $27 = $135, for $855 gross. Change the rule to daily overtime with two 10-hour days and the overtime bucket grows, so the gross changes too. ShiftTally shows the split — regular, overtime, double-time — next to the dollar figure, so the number is auditable instead of mysterious.
A few practical details make estimates more accurate. Round each day's hours the same way your payroll does — many systems round clock times to the nearest quarter hour, so a 9:02 clock-in becomes 9:00. Keep the workweek definition consistent: the FLSA workweek is any fixed 7-day period, and overtime is computed per workweek, not per pay period. And remember that salaried-exempt employees are not covered by these rules at all; overtime law applies to non-exempt hourly workers. ShiftTally's estimate assumes straight hourly pay with no shift differentials, bonuses, or tax withholding — it is a gross pay estimate for planning and verification, and your actual paycheck comes from your employer's payroll system.
Time card best practices for employees
The best time card habit is also the simplest: record times when they happen. Clock in when you start, clock out when you leave, and note your lunch break the same day. Reconstructing a week from memory on Friday afternoon is how phantom hours and missing breaks happen. If your employer rounds times, learn the rounding rule so your personal records match theirs — a five-minute daily gap becomes nearly half an hour a week. Keep your own copy: a quick photo of a paper time card, or your own entries in a tool like ShiftTally, gives you something to compare against your pay stub. Discrepancies are far easier to fix in the same pay period than two months later.
Watch your break deductions. The most common payroll complaint is a lunch break deducted on a day the employee worked through lunch. If you skipped lunch or took a shorter one, make sure the recorded break minutes reflect reality — with a time card calculator with lunch you can instantly see how a 60-minute versus 30-minute deduction changes your paid hours. Night-shift workers should double-check that overnight hours were credited to the right day; some systems assign them to the clock-in date and others to the clock-out date, and mixing conventions creates confusion that looks like missing pay.
Time card best practices for managers and small businesses
For managers, the weekly review is the control that matters. Before approving time cards, scan for the classic red flags: missing clock-outs, break minutes that are suspiciously identical every day, and days over 12 hours that might indicate a data-entry slip rather than a real shift. A weekly hours calculator with per-day breakdowns makes this review visual — the outlier day jumps out immediately. Approve in a consistent rhythm, ideally the day the week ends, so corrections happen while memories are fresh.
Choose your overtime rule deliberately and communicate it. If your state mandates daily overtime, your schedules and your calculator must both reflect it; if you operate under the federal weekly standard, make sure supervisors know that a 10-hour day alone does not create overtime. For businesses with several hourly staff, calculating each person's week separately and then aggregating — exactly what ShiftTally's multi-employee cards do — is far less error-prone than one giant spreadsheet where a single formula drag can corrupt every row. Export a CSV each pay period as your audit trail; it costs nothing and settles disputes in minutes.
Common time card mistakes (and how to avoid them)
Mistake one is the minutes-to-decimals error described earlier: 8:45 is 8.75 hours, not 8.45. Mistake two is forgetting the overnight rollover, which turns a 10 PM–6 AM shift into negative hours or zero. Mistake three is applying the wrong overtime rule — computing weekly overtime for employees covered by daily overtime law, or vice versa. Mistake four is deducting paid rest breaks as if they were lunch. Mistake five is rounding inconsistently, up one day and down the next. Every one of these is a pure arithmetic or rule-application error, which means every one of them disappears when the calculation is automated and the rule is explicit. That is the entire case for using a purpose-built time card calculator instead of mental math or a generic spreadsheet: the rules are encoded, the edge cases are handled, and the same inputs always produce the same answer.
One more subtle trap: mixing pay rates within a week. When an employee works two roles at different rates, the FLSA requires a blended “regular rate” for overtime purposes — you cannot simply pay all overtime at 1.5× the lower rate. ShiftTally keeps one rate per employee card, which covers the standard single-rate case cleanly; blended-rate situations should be verified against official guidance or your payroll provider. Similarly, holiday pay, PTO payouts, and shift differentials follow their own rules and sit outside basic time card math.
Why ShiftTally
Most free time calculators stop at “hours between two times.” ShiftTally was built for the real payroll week: seven day rows per employee, clock-in and clock-out with break minutes, automatic overnight-shift detection, and three selectable overtime rule sets including California double time. Add as many employee cards as you need — a whole small team fits on one page — and the totals sidebar aggregates regular hours, overtime, double time, and combined gross pay across everyone. Your week auto-saves to your device, so a closed tab never loses data, and one click prints clean time cards or exports a CSV for your records. It is free forever, with no signup, no paywall, and no watermark — just accurate time card math, every week.