How long is spotting normal after IUD insertion?

Varies. This, of course, varies for each patient. It is not uncommon to have spotting for a few days after insertion. It may even last a few weeks. With the Mirena (levonorgestrel) iud, because it has a low dose progesterone, it may even cause irregular cycles / spotting. .. This is not common, and the vast majority of patients report light periods or no periods.