HCG Levels

I found out I was having a miscarriage on August 9. I had already had brown spotting for a week before then, but I took cytotec that evening and started bleeding within a couple hours. I went for my follow-up yesterday and had blood work to test hcg levels. I had a voice mail when I got home that said I would have to retest next week. I know this is common, but how long did it take your levels to go back down?