In May 2026 the son-eomneun days fall on 5, 6, 15, 16, 25, 26. 6 in all. These are days whose lunar date ends in 9 or 0 — long the first thing people check before moving house or opening a shop.
May 1: 노동절; May 5: 어린이날; May 24: 부처님오신날; May 25: 대체공휴일(부처님오신날). Taken from Korea Astronomy and Space Science Institute open data.
May 5: 입하; May 21: 소만. Computed from the sun's ecliptic longitude, not looked up in a table.
These dates hold for every visitor. A son-eomneun day is fixed by the lunar calendar alone and has nothing to do with your birth chart. What a given day means for you needs a birth date — there is no auspicious day that holds for everybody.