Fingernails and Toenails on the Same Day
17. Some are careful not to cut the fingernails and toenails on the same day due to sakana (מגיד מישרים לב''י, הובא במג''א סי' ר''ס ומ''ב ). Here, too, there are some who are not careful about this (ה אריז''ל ), but the prevalent minhag is to be careful unless it is for a mitzva purpose, e.g., to remove a chatzitza. Thus, it is proper to cut the toenails on Thursday and the fingernails on Friday (שם ).
18. Although some are careful not to cut fingernails on Thursday (above, 4), there is no problem with cutting toenails on Thursday, as they are not so visible, so it is not noticeable that they are growing on Shabbos (מחצית השקל ). If one forgot to cut his toenails on Thursday, he should cut them on Friday with his fingernails (מטה אפרים סי' תרכ''ה ס''ג ), but it is best not to do both in the same sitting; there should be some break in between.
19. Night, then day. For this matter, the night is considered part of the following day, just like for all things in the Torah except karbonos. Thus, if one cut his fingernails on Tuesday afternoon, he may cut his toenails on Tuesday evening after tzeis hakochavim because that is considered a different day (א''א בוטשאטש סי' ר''ס ).
20. Some say that even if one cut his fingernails at night, he may cut his toenails the following day, as it is considered a different day regarding this (מילי דחסידותא על צוואת ר' יהודה החסיד סי' נ''ז ).
