Time Abbreviations
51 abbreviations · part of Units of Measurement Abbreviations
Abbreviations for units of time (s, min, h, d, wk, mo, yr), clock notation (AM, PM), business and fiscal periods (FY, Q1 to Q4, H1, YTD, YoY), calendar eras (AD, BC, CE, BCE, BP) and date formats such as MM/DD/YYYY and ISO 8601. Conventions vary: the SI symbols for second and hour are s and h, while everyday English prefers sec and hr, and the order of day and month in numeric dates differs between the United States and most other countries.
| Abbreviation | Stands for | Description |
|---|---|---|
| a | Annum (year) | Symbol for the year in scientific notation, from Latin annus, used mainly in geology, astronomy and nuclear physics. |
| a.m. | Ante meridiem (before midday) | Marks clock times from midnight up to noon in the 12-hour system used in the United States, Canada, Australia and much of the English-speaking world. |
| AD | Anno Domini (in the year of the Lord) | Label for years counted from the traditional year of Jesus' birth in the Western calendar, as in AD 1066. |
| BC | Before Christ | Label for years before the start of the Anno Domini era, counted backward so that larger numbers are earlier, as in 44 BC for the assassination of Julius Caesar. |
| BCE | Before the Common Era | Religiously neutral equivalent of BC, used in scholarship, museums, textbooks and Jewish writing for years before 1 CE, as in 586 BCE for the Babylonian destruction of… |
| BP | Before Present | Radiocarbon and archaeological dates counted backward from 1950, the reference year fixed because atmospheric nuclear tests later disturbed carbon-14 levels. |
| CE | Common Era | Religiously neutral label for the same years as AD, used in academic, scientific, Jewish and interfaith writing, as in 2026 CE. |
| CY | Calendar year | The January-to-December year, written out in budgeting, tax and insurance documents to distinguish it from a fiscal year or plan year. |
| d | Day | Symbol for the day, 24 hours or 86,400 seconds, accepted for use with SI. |
| DD | Day (two-digit, in date formats) | Placeholder for a two-digit day of the month, 01 to 31, in form instructions and date patterns such as DD/MM/YYYY. |
| DD/MM/YYYY | Day/month/year (date format) | The little-endian numeric date order used in the UK, Ireland, most of Europe, Latin America, India, Australia and much of Africa and Asia: 07/04/2026 means 7 April 2026. |
| FY | Fiscal year | The 12-month accounting period a government or company uses for budgets and financial reports, which need not match the calendar year. |
| h | Hour | The SI-accepted symbol for hour, 60 minutes or 3,600 seconds, used in scientific writing, timetables, compound units such as km/h and kWh, and clock times in several… |
| H1 | First half | First six months of a fiscal or calendar year, January through June for calendar-year companies. |
| H2 | Second half | Last six months of a fiscal or calendar year, July through December for calendar-year companies. |
| hh:mm:ss | Hours:minutes:seconds | Time-format pattern for hours, minutes and seconds separated by colons, as in 14:05:09, used in timestamps, video timecodes, race results and software settings. |
| hr | Hour | The most common abbreviation for hour in American everyday writing, used for business hours, parking rates, wages, rentals and medical notes. |
| hrs | Hours (military time) | Appended to 24-hour clock times in military, police, emergency-service and aviation writing, as in 0600 hrs or 1430 hrs. |
| ISO 8601 | International date and time standard (ISO 8601) | The International Organization for Standardization's standard for writing dates and times: year-month-day order, 24-hour time, week numbers, ordinal dates, time zone… |
| JD | Julian date (Julian Day number) | A continuous count of days used in astronomy, starting at noon Universal Time on 1 January 4713 BC in the proleptic Julian calendar. |
| kya | Thousand years ago | Abbreviation for dating recent prehistory such as human migrations and ice ages. |
| m | Minute (informal) | A single m after a number often means minutes in informal durations, video lengths and timestamps, as in 1h 30m or a 45m workout. |
| Ma | Megaannum (million years) | One million years, used in geology and paleontology for ages before the present: the dinosaurs other than birds died out about 66 Ma. |
| min | Minute | Sixty seconds, a sixtieth of an hour. |
| MM | Month (two-digit, in date formats) | Placeholder for a two-digit month, 01 to 12, in form instructions and software date patterns such as MM/DD/YYYY or YYYY-MM-DD. |
| MM/DD/YYYY | Month/day/year (US date format) | The numeric date order used in the United States, putting the month first: 07/04/2026 is July 4. |
| mo | Month | Used in prices, subscriptions, ages of babies and contract terms: $15/mo, a 6-mo-old, a 24-mo lease. |
| MoM | Month over month | Percentage change in a figure compared with the previous month, used for fast-moving metrics such as website traffic, subscription sales, retail sales and inflation. |
| ms | Millisecond | One thousandth of a second, the unit for network latency (ping), reaction times, audio delay, shutter lag and software performance. |
| MTD | Month to date | Cumulative figure from the first day of the current month up to today, used in sales dashboards, budgets, payroll and investment performance reports. |
| mya | Million years ago | Informal abbreviation common in popular science, museum labels, textbooks and documentaries. |
| ns | Nanosecond | One billionth of a second, the time scale of computer memory access and processor cycles. |
| p.m. | Post meridiem (after midday) | Marks clock times from noon until just before midnight on the 12-hour clock. |
| Q1 | First quarter | The first three months of a year: January through March for calendar-year companies. |
| Q2 | Second quarter | April through June in a calendar year, ending at the midpoint of the year. |
| Q3 | Third quarter | July through September in a calendar year. |
| Q4 | Fourth quarter | October through December in a calendar year, the final quarter and, for retailers, the most important, because it contains Black Friday, Cyber Monday and the holiday… |
| QoQ | Quarter over quarter | Comparison of a figure with the immediately preceding quarter, such as third-quarter sales against second-quarter sales, expressed as a percentage change. |
| QTD | Quarter to date | Cumulative figure from the start of the current quarter, calendar or fiscal, up to today, used in sales pipelines, budget tracking and fund performance reports. |
| qtr | Quarter | A three-month period of a year, used in business reports, tax filings, school calendars and sports. |
| s | Second | The SI base unit of time, defined since 1967 by the cesium-133 atom as exactly 9,192,631,770 periods of the radiation from a specific atomic transition. |
| sec | Second | Everyday abbreviation for second, common on stopwatches, recipes, workout plans, sports results and casual messages ("be there in a sec"). |
| T | Time designator (ISO 8601) | The letter that separates date from time in ISO 8601 timestamps, as in 2026-11-04T15:30:00Z. |
| wk | Week | Seven days. |
| WoW | Week over week | Percentage change in a metric compared with the previous week, common in e-commerce, app analytics, retail sales tracking and marketing dashboards. |
| YoY | Year over year | Comparison of a figure with the same period one year earlier, such as this quarter's revenue against the same quarter last year, expressed as a percentage change. |
| yr | Year | A calendar year of 365 days, or 366 in leap years, used in ages, warranties, interest rates and terms such as a 30-yr mortgage or a 5-yr plan. |
| YTD | Year to date | Period from the start of the current year, calendar or fiscal, up to the present date, used to report cumulative figures such as sales, earnings, investment returns or… |
| YY | Year (two-digit) | Two-digit year placeholder, as in MM/YY on credit card expiration dates or DD/MM/YY on receipts. |
| YYYY | Year (four-digit) | Four-digit year placeholder in date formats such as YYYY-MM-DD and MM/DD/YYYY, required on most official forms, databases and travel documents to avoid ambiguity about… |
| YYYY-MM-DD | Year-month-day (ISO 8601 date format) | The international standard date order defined in ISO 8601, running from the largest unit to the smallest: 2026-11-04. |
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- Metric and SI Unit Abbreviations (64)
- Month Abbreviations (12)
- Statistics Abbreviations (88)
- Time Zone Abbreviations (64)
- US Customary and Imperial Unit Abbreviations (43)