Time Calculator

Unlike ordinary decimal math, time uses base-60 for seconds and minutes. To add two durations (e.g., 2h 45m + 3h 30m), either convert both to total seconds or total minutes, add, then convert back: 165 + 210 = 375 minutes = 6 hours 15 minutes. Subtraction works the same way with borrowing: 3:15 − 1:45 requires borrowing an hour (60 minutes), giving 2:75 − 1:45 = 1:30. Our calculator does all of this internally and shows three equivalent representations at once: HH:MM:SS (natural reading), total minutes (easy to multiply), and decimal hours (standard for payroll and billing). Understanding the underlying base-60 system helps you spot errors — for example, a result showing 8:75 is wrong; it should be 9:15.

Time difference is the most common time-calculator use case: you have a start time and an end time and need to know how long elapsed. Convert both to minutes-since-midnight (hour × 60 + minute), subtract start from end, and convert back. Example: 9:00 AM to 5:30 PM = (17×60 + 30) − (9×60) = 1050 − 540 = 510 minutes = 8h 30m. This handles any same-day pair correctly. For AM/PM input, convert to 24-hour first: 9:00 AM stays as 09:00, 5:30 PM becomes 17:30, 12:00 AM (midnight) is 00:00, 12:00 PM (noon) is 12:00. The calculator accepts either 12-hour with AM/PM or 24-hour input and unifies internally.

Overnight shifts are the classic gotcha: 10:00 PM to 6:00 AM. Naively subtracting gives a negative number (6 − 22 = −16 hours). Fix: when end time appears before start time, add 24 hours to the end, then subtract. 6:00 AM + 24h = 30:00; 30:00 − 22:00 = 8 hours. Our calculator detects this automatically when you enter times where end < start, and the displayed duration will correctly reflect the overnight span. Common real-world examples: hospital night shifts (7 PM to 7 AM = 12 hours), restaurant closing shifts (4 PM to 2 AM = 10 hours), and security/third shift (11 PM to 7 AM = 8 hours). For shifts longer than 24 hours, add 48 hours and confirm the result is reasonable.

Decimal hours express a duration as a fraction of an hour, used in payroll systems, billing software and spreadsheets because they multiply cleanly with hourly rates. Conversion: decimal = total_minutes ÷ 60. Common equivalents: 15 min = 0.25, 20 min = 0.333, 30 min = 0.5, 45 min = 0.75. Reverse: multiply the fractional part by 60 to get minutes. 1.5 hours = 1 hour + 0.5 × 60 = 1h 30m (not 1h 50m — the most common decimal-hours mistake). Examples in practice: 8.5 hours × $20/hour = $170; a project logged as 42.75 hours = 42h 45m. Our calculator shows decimal hours alongside HH:MM:SS so you can pick whichever format your system requires.

Most payroll calculations start with a gross time (clock-in to clock-out), then subtract unpaid breaks to get net paid hours. Example: clock-in 8:00 AM, clock-out 5:30 PM (gross 9.5 hours), unpaid 30-minute lunch (0.5 hours), net 9.0 hours paid. Break rules vary by jurisdiction: US federal law doesn't mandate paid breaks, but short rest breaks (5–20 minutes) are usually paid; meal breaks (30+ minutes) can be unpaid if the employee is fully relieved of duties. California requires paid 10-minute rest breaks per 4 hours and unpaid 30-minute meal breaks before 5 hours worked. UK: 20-minute break after 6+ hours (usually unpaid). Canada federal: 30-minute break after 5+ hours. Australia: meal breaks depend on the relevant award. Enter break duration in our Time Difference mode to see net work time alongside gross.

United States: The Fair Labor Standards Act (FLSA) does not cap daily or weekly hours for adult workers but requires overtime pay (1.5× regular rate) for non-exempt workers over 40 hours per workweek. States like California layer additional rules: daily overtime after 8 hours, double-time after 12. United Kingdom: Working Time Regulations 1998 cap average weekly hours at 48 measured over a 17-week reference period; workers aged 18+ may opt out in writing. Statutory rest breaks: 11 hours daily, 24 hours weekly, 20-minute break on shifts over 6 hours. Canada: The federal Canada Labour Code applies to federally-regulated sectors (banks, telecom, interprovincial transport) and caps standard hours at 40/week with overtime after. Provincial rules govern most workers — Ontario allows up to 48 hours/week, Alberta 44, etc. Australia: The National Employment Standards (NES) limit ordinary hours to 38/week, plus 'reasonable additional hours' determined by factors like employee safety and family obligations. Modern awards and enterprise agreements add overtime rates and shift loadings.

US (FLSA): 1.5× regular rate after 40 hours/week for non-exempt employees. Exempt categories (salaried executives, professionals, outside sales) don't get overtime. State variations can be stricter — California: 1.5× after 8 hrs/day, 2× after 12; 7th consecutive day triggers 1.5× for first 8 hrs, 2× after. UK: No statutory overtime premium — overtime pay (if any) is contractual. Workers must consent to exceed the 48-hour average, and rest period rules still apply. Canada: Federal sector — 1.5× after 40 hours/week or 8 hours/day, whichever is less. Provincial thresholds differ: Ontario 44 hrs/week, Alberta 44 hrs/week or 8 hrs/day. Australia: Most modern awards pay 1.5× for first 2–3 overtime hours, then 2×. Weekend, public holiday and evening shifts often carry additional penalty rates (typically 1.5×–2.5×). Always verify against the specific award or enterprise agreement covering the role.

The 12-hour clock is standard in the US, Canada, Australia and UK for everyday use, splitting the day into AM (ante meridiem, before noon) and PM (post meridiem, after noon). The 24-hour clock (sometimes called military time) runs 00:00 through 23:59 and is the international standard for aviation, medicine, military operations, programming and logistics. Conversion: 12:00 AM = 00:00, 1:00 AM = 01:00, ..., 12:00 PM = 12:00, 1:00 PM = 13:00, ..., 11:00 PM = 23:00. To convert PM hours to 24-hour, add 12 (except 12:00 PM which stays 12:00). The 24-hour clock eliminates the 12 AM vs 12 PM ambiguity entirely — schedule '00:00' or '24:00' for midnight, '12:00' for noon with no confusion.

ISO 8601 is the unambiguous format for date and time used across international business, software, databases and APIs: YYYY-MM-DDTHH:MM:SS, optionally with a time-zone offset. Example: 2026-04-24T15:30:00-05:00 means 24 April 2026 at 3:30 PM US Eastern. The literal 'T' separates date from time. UTC is denoted with 'Z' (e.g., 2026-04-24T20:30:00Z). Advantages over regional formats: sorts chronologically as plain text, removes DD/MM vs MM/DD ambiguity (a long-running US/UK confusion), works across locales, and is machine-parseable everywhere. Most programming languages and databases default to ISO 8601 — JSON APIs, log files, PostgreSQL, JavaScript Date.toISOString() all use it. If you're sharing date-time data across systems or countries, use ISO 8601.

A time zone is a region where all clocks observe the same civil time, offset from Coordinated Universal Time (UTC). Major zones relevant to our target markets: US Eastern UTC-5/-4 (EST/EDT), US Pacific UTC-8/-7 (PST/PDT), UK UTC+0/+1 (GMT/BST), Central Europe UTC+1/+2 (CET/CEST), Sydney UTC+10/+11 (AEST/AEDT), Toronto UTC-5/-4. Daylight Saving Time shifts the clock forward 1 hour in spring, back in autumn, to extend daylight during waking hours — but not every region observes it. Australia DST: NSW, VIC, SA, TAS, ACT observe; QLD, WA, NT do not. US: Hawaii and most of Arizona do not observe. When calculating durations across DST boundaries, work in UTC or elapsed time — otherwise you may accidentally add or subtract an extra hour. The safest pattern: convert all times to UTC, do arithmetic, convert results to the recipient's local time.

Confusing 12 AM with 12 PM. 12:00 AM is midnight (start of day), 12:00 PM is noon. Setting a meeting for '12 PM' that actually runs at midnight has embarrassed many a calendar app. Mishandling the 60-minute rollover. Writing '8:75' instead of '9:15' when adding times manually — always carry minutes over 60 into hours. Decimal hours errors. 1.5 hours is 1h 30m, not 1h 50m. The decimal portion represents fractions of 60, not 100. Ignoring overnight shifts. Calculating 10 PM to 6 AM as 6 − 22 = −16 hours without adding 24 to the end. Always verify: if your time-difference result is negative or over 24 hours, something's wrong. Forgetting unpaid breaks. Gross time is clock-in to clock-out; net time subtracts breaks. Your paycheck depends on net. Mixing time zones. Adding 9 AM New York to 3 PM London without converting first — the two times are actually 2 hours apart, not 6. Always work in one zone (preferably UTC) when doing arithmetic.