Cron expression parser and explainer

Translate a five-field cron expression or crontab line into plain English and list its next run times after any start date and time, in UTC.

Обновлено 28 сентября 2026 г.Проверенные примеры: 7

Next run

Tue 2026-09-29 09:00 UTC

In plain English: Every 15 minutes, during hours 09 through 17, on Monday through Friday
Upcoming runs: Tue 2026-09-29 09:00 UTC Tue 2026-09-29 09:15 UTC Tue 2026-09-29 09:30 UTC Tue 2026-09-29 09:45 UTC Tue 2026-09-29 10:00 UTC Tue 2026-09-29 10:15 UTC Tue 2026-09-29 10:30 UTC Tue 2026-09-29 10:45 UTC Tue 2026-09-29 11:00 UTC Tue 2026-09-29 11:15 UTC
Time until the next run: 9 h
Runs on each matching day: 36

Times are UTC. A cron daemon uses its server's time zone (or CRON_TZ), so shift these if the server isn't on UTC.

Every 15 minutes, during hours 09 through 17, on Monday through Friday. The next run after the start is Tue 2026-09-29 09:00 UTC, followed by Tue 2026-09-29 09:15 UTC.

Next runs

Upcoming runs (UTC) Строк: 10

#	Run
1	Tue 2026-09-29 09:00 UTC
2	Tue 2026-09-29 09:15 UTC
3	Tue 2026-09-29 09:30 UTC
4	Tue 2026-09-29 09:45 UTC
5	Tue 2026-09-29 10:00 UTC
6	Tue 2026-09-29 10:15 UTC
7	Tue 2026-09-29 10:30 UTC
8	Tue 2026-09-29 10:45 UTC
9	Tue 2026-09-29 11:00 UTC
10	Tue 2026-09-29 11:15 UTC

Как выполняется расчёт S

Minute: */15
4 values: 0, 15, 30, 45.
Hour: 9-17
9 values: 9, 10, 11, 12, 13, 14, 15, 16, 17.
Day of month: *
Every day of month.
Month: *
Every month.
Day of week: MON-FRI
5 values: Mon, Tue, Wed, Thu, Fri.
Combine the two day fields
At least one day field starts with *, so a day must match both (with * matching everything).
Scan forward
Starting after 2026-09-29 00:00 UTC, check each day, then each matching hour and minute, until 10 runs are found.

О калькуляторе: Cron expression parser and explainer

A cron expression has five fields: minute (0–59), hour (0–23), day of month (1–31), month (1–12 or JAN–DEC) and day of week (0–7 or SUN–SAT, where 0 and 7 both mean Sunday). Each field takes a single value, a comma-separated list, a range with a hyphen or a step with a slash. The parser expands every field into its set of values, then scans forward day by day for the minutes that match all five.

The default, */15 9-17 * * MON-FRI, runs every 15 minutes from 09:00 to 17:45 on weekdays, which is 36 runs on each matching day. Started at midnight on Thursday 15 January 2026, its first run is 09:00 that morning.

When day of month and day of week are both restricted, cron runs on days that match either one, as crontab(5) specifies. Times here are UTC; a cron daemon uses its server's time zone, or CRON_TZ in cronie.

Примеры с решением

Every 15 minutes in office hours

Выражение cron: */15 9-17 * * MON-FRI
Start date (UTC): 2026-01-15
Start time (UTC): 00:00

Next run: Thu 2026-01-15 09:00 UTC
Upcoming runs: Thu 2026-01-15 09:00 UTC Thu 2026-01-15 09:15 UTC Thu 2026-01-15 09:30 UTC Thu 2026-01-15 09:45 UTC Thu 2026-01-15 10:00 UTC Thu 2026-01-15 10:15 UTC Thu 2026-01-15 10:30 UTC Thu 2026-01-15 10:45 UTC Thu 2026-01-15 11:00 UTC Thu 2026-01-15 11:15 UTC
Runs on each matching day: 36
Time until the next run: 9 h

Источник проверки: Brute-force Python 3.8 datetime scan minute by minute with an independent field parser; 4 minutes × 9 hours = 36 runs a day; 09:00 − 00:00 = 32400 s

Daily at 09:00, starting exactly at 09:00 (edge)

Выражение cron: 0 9 * * *
Start date (UTC): 2026-01-15
Start time (UTC): 09:00
Runs to list: 3

Next run: Fri 2026-01-16 09:00 UTC
In plain English: At 09:00, every day
Upcoming runs: Fri 2026-01-16 09:00 UTC Sat 2026-01-17 09:00 UTC Sun 2026-01-18 09:00 UTC

Источник проверки: crontab(5): runs are strictly after the start; confirmed by the Python brute-force scan

Leap day only

Выражение cron: 0 0 29 2 *
Start date (UTC): 2026-01-15
Start time (UTC): 00:00
Runs to list: 3

Next run: Tue 2028-02-29 00:00 UTC
Upcoming runs: Tue 2028-02-29 00:00 UTC Sun 2032-02-29 00:00 UTC Fri 2036-02-29 00:00 UTC

Источник проверки: Python 3.8 calendar.isleap and datetime weekday, via the brute-force scan

Day 1 or Monday (both day fields restricted)

Выражение cron: 0 12 1 * MON
Start date (UTC): 2026-01-15
Start time (UTC): 00:00
Runs to list: 5

Upcoming runs: Mon 2026-01-19 12:00 UTC Mon 2026-01-26 12:00 UTC Sun 2026-02-01 12:00 UTC Mon 2026-02-02 12:00 UTC Mon 2026-02-09 12:00 UTC

Источник проверки: crontab(5) OR rule for day-of-month and day-of-week, checked by the Python brute-force scan

Вопросы

What does */5 mean in a cron expression?

*/5 means every 5th value of the field, counted from the field's first value. In the minute field it fires at minutes 0, 5, 10 … 55, which is 12 times an hour. A step can follow a range too: 10-30/10 gives minutes 10, 20 and 30. Steps restart each hour, so */7 runs at minute 56 and then again at minute 0.

How do I run a cron job every day at midnight?

Write 0 0 * * *, which means minute 0 of hour 0 on every day, or use the @daily macro, which cronie and Vixie cron expand to the same five fields. For 2:30 a.m. every day write 30 2 * * *, and for 09:00 on weekdays write 0 9 * * 1-5. The hour is read in the server's time zone unless the crontab sets CRON_TZ.

How do day of month and day of week combine in cron?

If both fields are restricted, cron runs when either one matches, so 0 12 1 * MON fires at noon on the 1st of every month and on every Monday. In Vixie cron and cronie, a day field that starts with * switches this to both, which is why 0 0 */2 * FRI runs only on Fridays that fall on odd dates such as the 23rd.

Why does my cron expression have 6 or 7 fields?

Standard cron uses 5 fields. Quartz and Spring schedulers put a seconds field in front, making 6, and Quartz accepts an optional year as a 7th, so an expression like 0 0/15 * * * ? belongs to those tools rather than crontab; the ? placeholder is Quartz syntax. This parser reads the 5-field crontab format plus the @hourly, @daily, @weekly, @monthly and @yearly macros.

Can cron run a job every 30 seconds?

Not directly: the smallest unit in a crontab is 1 minute, because the first field is the minute. The usual workaround is two entries, * * * * * job and * * * * * sleep 30; job, which start the job at 0 and 30 seconds past each minute. systemd timers accept OnCalendar schedules down to the second if you need finer control.

Насколько точен «Cron expression parser and explainer»?

Точность зависит от введённых данных и допущений метода. Десятичная арифметика использует 50 значащих цифр, но оценки, численные методы и исходные данные могут быть менее точными; округление на экране не устраняет эти ограничения. Решённые примеры, проверенные по независимым источникам: 7. Например, «Every 15 minutes in office hours» проверяется по источнику Brute-force Python 3.8 datetime scan minute by minute with an independent field parser; 4 minutes × 9 hours = 36 runs a day; 09:00 − 00:00 = 32400 s.

Откуда взята методика?

POSIX.1-2017 (IEEE Std 1003.1) — crontab utility, input file format; crontab(5) — cronie / Vixie cron: ranges, steps, names, @ macros and the day-of-month / day-of-week rule.

Об этом калькуляторе

\begin{aligned} \text{run} &\iff m \in M \land h \in H \\ &\qquad \land\ \text{month} \in Mo \land \text{day} \\ \text{day} &= \begin{cases} \text{DOM} \lor \text{DOW} & \text{both} \ne * \\ \text{DOM} \land \text{DOW} & \text{otherwise} \end{cases} \end{aligned}

Источники

Проверено по источникам

В калькулятор включены решённые примеры с ответами из независимых источников. Их количество: 7. Они входят в набор тестов, и вы также можете запустить их здесь.

Next runs

Minute: */15

Hour: 9-17

Day of month: *

Month: *

Day of week: MON-FRI

Combine the two day fields

Scan forward