0 0 1,15 * * — twice a month

Answer

0 0 1,15 * * runs at 00:00 on the 1st and the 15th of every month: 24 times a year.

At 00:00 on day 1 and 15 of the month.

0
Minute (0-59)
At minute 0 (on the hour)
0
Hour (0-23)
Hour 0 (midnight, 00:00–00:59)
1,15
Day of month (1-31)
The 1st of the month or the 15th of the month
- 1 the 1st of the month
- 15 the 15th of the month
*
Month (1-12 or JAN-DEC)
Every month
*
Day of week (0-7 or SUN-SAT (0 and 7 = Sunday))
Every day (no restriction)

0.07 runs a day on average0.46 a week24 of the next 364 days have a run

Hours of the week (darker = more runs)

The next 52 weeks, one square per day

What to know

A comma makes a list. Lists can mix single values and ranges, like 1,15,28-31.

0 9 1,15 * *
the 1st and 15th at 09:00At 09:00 on day 1 and 15 of the month.

Semi-monthly is not every two weeks: the gap is 14 days in February and up to 17 days in 31-day months.