Is it normal to have an hcg level of 6.6 6 days before your missed period?

You are right on the border line. Less than 5 is considered not pregnant but anything over 25 is pregnant for sure. So I'd advise waiting another few days and then either your period will come or you can do another hcg test which should be higher (in theory).

In terms of pregnancy the hcg levels vary from week to week.
I found this which you might find helpful:
3 weeks LMP: 5 - 50 mIU/ml
4 weeks LMP: 5 - 426 mIU/ml
5 weeks LMP: 18 - 7,340 mIU/ml
6 weeks LMP: 1,080 - 56,500 mIU/ml
7 - 8 weeks LMP: 7, 650 - 229,000 mIU/ml
9 - 12 weeks LMP: 25,700 - 288,000 mIU/ml
13 - 16 weeks LMP: 13,300 - 254,000 mIU/ml
17 - 24 weeks LMP: 4,060 - 165,400 mIU/ml
25 - 40 weeks LMP: 3,640 - 117,000 mIU/ml
Non-pregnant females: <5.0 mIU/ml
Postmenopausal females: <9.5 mIU/ml

Quote:

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Originally Posted by Gernald

You are right on the border line. Less than 5 is considered not pregnant but anything over 25 is pregnant for sure. So I'd advise waiting another few days and then either your period will come or you can do another hcg test which should be higher (in theory).

In terms of pregnancy the hcg levels vary from week to week.
I found this which you might find helpful:
3 weeks LMP: 5 - 50 mIU/ml
4 weeks LMP: 5 - 426 mIU/ml
5 weeks LMP: 18 - 7,340 mIU/ml
6 weeks LMP: 1,080 - 56,500 mIU/ml
7 - 8 weeks LMP: 7, 650 - 229,000 mIU/ml
9 - 12 weeks LMP: 25,700 - 288,000 mIU/ml
13 - 16 weeks LMP: 13,300 - 254,000 mIU/ml
17 - 24 weeks LMP: 4,060 - 165,400 mIU/ml
25 - 40 weeks LMP: 3,640 - 117,000 mIU/ml
Non-pregnant females: <5.0 mIU/ml
Postmenopausal females: <9.5 mIU/ml

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- Great info, worth saving. A "like" and applause.