My son is filing his own taxes and can't be considered my dependent since he made over $5,000, but was on my Marketplace insurance, so can you help on percentages?

[BillM223]

The percentages can be anything you want, so long that the percentages add up to 100% among all the parties.

In your case, it is common that the primary taxpayer take 100% and the others 0%, because the primary taxpayer usually has the largest income, pays the ACA insurance premiums, and gets the most benefit from the Premium Tax Credit (PTC) (the money paid by the federal government to the insurance company to assist you in paying the health insurance premiums). This also means that the primary taxpayer would be on the hook for any PTC shortfall or get any refund of PTC underpayment.

But, as I say, it can absolutely be arranged any way you want.