Wendy said: You have to go based on their serum level. Generally 5000iu daily, but in my own case, for instance, that amount won't keep me in my preferred range of 60-80, so during the winter, I take 5000iu every day and around 3x per week I double it. You just have to keep checking labs and adjusting dose as needed. Don't let the D stay over 100 in the serum for very long!