The date and time formats you meet in code, logs and APIs. Every example is for the single instant Saturday October 3, 2026 at 14:30:05 UTC, produced by running the code. Convert with the Date Calculator, Time Duration Calculator and Time Zone Calculator.
ISO 8601, the unambiguous standard
| Format | Meaning |
|---|---|
2026-10-03 |
Calendar date |
2026-10 |
Year and month |
2026-W40-6 |
Week date: week 40, day 6 (Saturday) |
2026-276 |
Ordinal date: day 276 of the year |
14:30:05 |
Time of day |
2026-10-03T14:30:05Z |
Date and time in UTC (Z means zero offset) |
2026-10-03T16:30:05+02:00 |
The same instant at UTC+2 |
P1Y2M3DT4H5M6S |
Duration: 1 year, 2 months, 3 days, 4 hours, 5 minutes, 6 seconds |
2026-10-03/2026-10-10 |
Time interval |
Prefer ISO 8601 for storing and exchanging dates: it sorts correctly as text and has one meaning everywhere, unlike 03/10/2026, which is 3 October in most of the world and 10 March in the US. Week dates and week numbers come from the Week Number Calculator; the weekday of any date from the Day of the Week Calculator.
strftime codes
These codes work in Python, C, PHP, Ruby and most shells (a few, such as %e and %f, vary by platform).
| Code | Meaning | Result |
|---|---|---|
%Y |
year, four digits | 2026 |
%y |
year, two digits | 26 |
%m |
month 01 to 12 | 10 |
%B |
month name | October |
%b |
month abbreviation | Oct |
%d |
day of month 01 to 31 | 03 |
%e |
day of month, space padded | 3 |
%j |
day of year 001 to 366 | 276 |
%A |
weekday name | Saturday |
%a |
weekday abbreviation | Sat |
%u |
weekday 1 (Monday) to 7 | 6 |
%H |
hour 00 to 23 | 14 |
%I |
hour 01 to 12 | 02 |
%p |
AM or PM | PM |
%M |
minute 00 to 59 | 30 |
%S |
second 00 to 59 | 05 |
%f |
microseconds | 000000 |
%z |
UTC offset | +0000 |
%Z |
time zone name | UTC |
%V |
ISO week number | 40 |
%G |
ISO week-based year | 2026 |
%% |
a literal percent sign | % |
Unix time
| Unit | Value for 2026-10-03T14:30:05Z |
|---|---|
| Seconds (Unix time, most APIs) | 1791037805 |
Milliseconds (JavaScript Date.now()) |
1791037805000 |
| Microseconds | 1791037805000000 |
| Days since 1970-01-01 | 20729 |
Unix time counts seconds since 1970-01-01T00:00:00Z (Unix timestamp). Always say whether a number is in seconds or milliseconds: a 10-digit value is seconds, a 13-digit value is milliseconds.
Pitfalls
- Leap years. A year is a leap year if divisible by 4, except centuries, unless divisible by 400: 2000 and 2024 are leap years; 1900 and 2100 are not.
- ISO week years. Dates near New Year can belong to the neighbouring year's week: 1 January 2027 is in week 53 of 2026.
- Daylight saving time. Local clock times can repeat or not exist for an hour; store UTC and convert for display.
- Duration versus clock time. Use the Time Calculator for durations in hours and minutes, the Hours Calculator for time-card totals, the Day Counter for days between dates, and the Age Calculator for exact ages. The Military Time Converter and Sleep Calculator cover 24-hour clocks and sleep cycles.