How long for hcg to get back to zero?

Judy

I had a d&c midnight on Sunday for missed miscarriage, baby had heartbeat at 6wk2days, I was almost 8weeks and had some strong contraction like cramps so I went to ER, to find out the baby heart had stopped

My hcg was 20,000

How long could it take for my hcg to go back to zero?

I did a test this morning and it’s still very positive

This is my 7th loss

Today I’m coping better then the last few days

Thank you