How to use
Pick a view at the top.
- Calendar: you start with today’s date and this month’s calendar. Each date shows its lunar day in small type underneath, and son-free days are shaded and marked “free”. Tap a date to see its lunar date and the direction of son. For a day with son, the next son-free day is also shown. Use the ‹ › buttons to go to the previous or next month, or type any date into the date field.
- List: shows the son-free days from today through the next 3, 6 or 12 months, with the solar date (including the day of the week) and the lunar date. Turn on “Weekends only” to keep just the son-free days that fall on a Saturday or Sunday. There’s no public holiday data, so holidays aren’t marked. Press “Copy list” to copy the list as text and paste it into a message or note.
What is a son-free day?
“Son” (손) is a spirit that, in Korean folk belief, moves between east, west, south and north depending on the date, getting in the way of people’s plans and doing them harm. The National Folk Museum of Korea’s Encyclopedia of Korean Folk Culture explains “son” as a shortened form of “sonnim” (guest), and the Encyclopedia of Korean Culture identifies it with taebaeksal (太白煞), a baleful spirit found in Chinese divination books. A “son-free day” (son eomneun nal, 손 없는 날) is a day when son is in no direction at all, so it’s believed no harm will come.
Son-free days are a traditional custom (a folk belief) with no scientific basis. This calendar only finds the dates according to the custom; it doesn’t judge any day as good or bad.
The rule: the last digit of the lunar date
Son-free days are set by the last digit of the lunar date, not the solar date. Days ending in 9 or 0 are son-free: lunar days 9, 10, 19, 20, 29 and 30.
A lunar month has 29 or 30 days, so it contains five or six son-free days. Solar months have different boundaries, so the dates and counts vary between solar months.
The direction of son
Son moves to a new direction every two days according to the last digit of the lunar date, going all the way around every 10 days.
| Last digit of lunar day | Days | Direction of son |
|---|---|---|
| 1 · 2 | 1, 2, 11, 12, 21, 22 | East |
| 3 · 4 | 3, 4, 13, 14, 23, 24 | South |
| 5 · 6 | 5, 6, 15, 16, 25, 26 | West |
| 7 · 8 | 7, 8, 17, 18, 27, 28 | North |
| 9 · 0 | 9, 10, 19, 20, 29, 30 | None (son-free day) |
The Encyclopedia of Korean Folk Culture says that on days ending in 9 or 0, son has gone up to the sky and is in no direction. The Encyclopedia of Korean Culture says son is in the sky on days 9, 19 and 29 and in the earth on days 10, 20 and 30; either way, son is in none of the four directions.
Lunar calendar basis and supported range
Lunar dates follow the Korean lunar calendar published by the Korea Astronomy and Space Science Institute (KASI). This calendar uses the same basis and the same conversion table as this site’s Korean lunar calendar converter (the open-source library korean-lunar-calendar, MIT License). In some months, day 1 of the Korean lunar month is one day off from the Chinese lunar calendar, so a son-free day found with a Chinese calendar can differ by one day.
Supported dates run from January 31, 1900 to December 31, 2050. In the list view, if the period goes past December 31, 2050, only the dates up to that day are shown.