Is there an issue of being paid interest from the bank on shabbos or on shabbos going into yom tov?
When one is paid interest from a bank for a savings account etc., the bank pays the interest by paying a small part of the yearly interest rate every day. Receiving this money can occasionally be considered שכר שבת. The contemporary Poskim say say that the interest accrued on an ordinary Shabbos may be used and is not שכר שבת because the bank pays the interest according to the calendar date from 12 am to 12 am. Therefore, part of the interest is for Friday or מוצאי שבת which is הבלעה and permitted. However, when there are two days of קודש such as a the two days of ראש השנה, or when Yom Tov occurs on Friday or Sunday, then one of the days’ worth of interest is definitely from a holy time and should not be benefited from. One option is to put the money into צדקה privately so no one will know about it and the person will not get any recognition for it, which would be considered benefiting from it.
Note: on a regular Yom Tov, when there are two days, R’ Moshe zt”l ruled that one may benefit from the interest of both days. Since the custom of observing two days is because in the time of בית דין the people in the Diaspora didn’t know the exact day of the lunar month (see הלכות ראש השנה- ), therefore both days are observed. However, since one of the days is not “really” the holy one, the other day is considered (only for these הלכות) as the only one holy day. On ראש השנה however both days are considered holy.
 ע’ אג”מ או”ח ח”ד ס’ נ”ט, מנח”י ח”ט ס’ נ”ט, באר משה ח”ה ס’ ק’, בצל החכמה ח”ג ס’ ל”ח וע’ שש”כ פ’ כ”ח הערה ק”י מרש”ז זצ”ל שלפי הגר”ח יהיה כל הריבית מותר.