When should I be concerned for a late period?

How many days late should my period be in order for me to be concerning? I have a copper IUD and my period is a few days late. I had my IUD for 7 years. When should I see a doctor if my period doesn’t come? How late should it be for it to be unhealthy? What causes a super late period on the copper IUD? Besides pregnancy because I can’t be pregnant on the IUD.

When should I be concerned for a late period?
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