I assume you are talking about the Premium Tax Credit (PTC) form 8962. If I recall correctly (and I may very well be wrong here), contribution/credit limits are figured "per month". So you only have to pro-rate monthly contributions from July thru Dec. assuming your daughter no longer qualifies for your plan starting in July. (Just because she may have moved out, may not mean she no longer qualifies. You're really not provided enough details on that, such as why she moved out, or why she no longer qualifies for your HDHP)
If you look at the form 8962 (sample at https://www.irs.gov/pub/irs-pdf/f8962.pdf) You'll see the credit is figured monthly, beginning on line 12 of that form.
