In other words, would my partner owe tax on that if we own the account jointly? Would the situation change if it were a brokerage account owned jointly? Thanks for your opinion.
If you are reeceiving no consideration for it, i.e., no goods or services, then is is a gift, not income, and no imcome tax would be due from him. You might owe gift taxes. If the gift is less than $13,000, it is exempt--no tax. If more then you should file a gift tax return, but you will not owe gift taxes unless the gift is in seven figures, because it just comes off your lifetime gift tax applicable amount. See an estate planning lawyer if the gift exceeds $13,000. (This answer does not take into account the recent tax law changes in amounts of of the exemption and exclusion.)
DISCLAIMER—This answer is for informational purposes only under the AVVO system, its terms and conditions. It is not intended as specific legal advice regarding your question. The answer could be different if all the facts were known. This answer does not establish an attorney client relationship. I am admitted only in California.
(Bryant) Keith Martin