Question: I made a vow to give a certain amount to tzedakah, but I don’t remember how much I pledged. What should I do?

Answer: Shulchan Aruch (Yoreh De'ah 258:3) states: "One who vows to give tzedakah but does not remember how much he pledged must continue giving generously until he is certain he has given the full amount he intended."

However, later authorities (Aruch HaShulchan and others) write that if one wishes, they may perform hatarat nedarim (annulment of vows) to be released from the uncertainty.