Cron Expression Parser

Written byOleh Soloninupdated 5 October 2026

Cron expression

Result

Field breakdownMinute 0 · Hour 9 · Day * · Month * · Weekday 1-5
Minutesat 0
Hoursat 9
Day of monthevery day of the month
Monthevery month
Day of weekMonday to Friday

Five fields, read one at a time

Break a cron expression into its five fields and read what each one does, so you know when the job really runs.

Cron packs a schedule into five terse fields: minute, hour, day of month, month and day of week. Reading it wrong is how a job meant for once a week ends up running every day.

The classic trap is combining day-of-month and day-of-week. Most cron implementations treat those two as OR rather than AND, so specifying both runs the job on either match.

How to use

Enter a five-field expression: minute, hour, day of month, month, day of week.
Check the field-by-field reading: it shows what the expression really means rather than what was intended.
If the summary line carries a warning about OR, reread the two day fields — that is where almost every surprise run comes from.

Expressions that cover almost everything

A star means "any value", a slash a step, a hyphen a range and a comma a list. Standard cron has no other symbols, and almost any schedule can be built from those four.

Weekdays are numbered from zero, and Sunday has two numbers: 0 and 7. That is a historical accident, and the parser accepts both.

Every row comes from the parser on this page. Until recently it printed a weekday numbered 7 as a bare digit instead of recognising it as Sunday.
Expression	Day of month	Day of week
0 9 * * 1-5	every day of the month	Monday to Friday
0 0 1 * *	at 1	any day of the week
0 0 1,15 * *	at 1, 15	any day of the week
30 2 * * 7	every day of the month	Sunday
0 9 * * 6,0	every day of the month	Saturday, Sunday

The trap that catches everyone once

Day of month and day of week are the only two fields not joined by AND. When both are restricted, cron joins them with OR: the job runs on any day that satisfies either condition.

"0 0 1-7 * 1" reads like "the first Monday of the month" and means something else entirely: every day from the 1st to the 7th, and every Monday besides. The parser says so in its summary line as soon as both fields are set.

On the third row the parser on this page prints its warning about OR. The behaviour is written into the POSIX specification and is not an implementation bug; "the first Monday" cannot be expressed in plain cron and is checked inside the job instead.
Expression	What people usually mean	What cron does
0 0 1 * *	the first of the month	the first of the month
0 0 * * 1	every Monday	every Monday
0 0 1-7 * 1	the first Monday of the month	any day from the 1st to the 7th OR any Monday

What this calculator shows

Each of the five fields explained separately
Weekday numbers translated into day names
Ranges, lists and step values interpreted

What to keep in mind

Covers standard five-field cron; six-field variants with seconds are not parsed.
Cron runs in the server's timezone, which is a frequent source of off-by-hours surprises.

FAQs

What does */5 mean?

Every fifth unit of that field. In the minutes position it means every five minutes: 0, 5, 10 and so on. Counting starts at the beginning of the range, not at the moment the job was installed.

How do I run something once a month?

Fix the day of month and leave day of week as a star: 0 3 1 * * runs at 03:00 on the first of every month.

Why did my job run on the wrong day?

Most likely the day-of-month and day-of-week fields are both set. Standard cron treats that as OR, so the job fires on either condition. The parser warns about it in the summary line.

How do I run a job on the first Monday of the month?

Not with cron alone: "0 0 1-7 * 1" fires every day from the 1st to the 7th and every Monday on top. The usual approach is to run the job every Monday and have it exit unless the day of the month is seven or less.

Is Sunday 0 or 7?

Both. The day-of-week field accepts either number; seven is a later extension that caught on. The parser understands both and names the day in words.

Which timezone does cron use?

The server's local time unless configured otherwise. Containers frequently default to UTC, which is why a job set for 09:00 can run hours off. Where the clocks change for summer, a job can be skipped or run twice on the night they change.

Worked example

A weekday morning job

Input: 0 9 * * 1-5

Output: At 09:00, Monday through Friday

Note: Change the first field to */15 and it runs every fifteen minutes during those hours instead — a very different load on your system.

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Cron Expression Parser

Result

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