due to the special tax rates afforded long-term capital gains and qualified dividends you could owe $0 on the capital gain. if you have a state tax you might owe the state.
there is no way for us to know whether it would be cheaper to sell in Dec '21 vs Jan '22
you may need to do some tax projections based on where you think you'll be for 2021 and do your best to estimate 2022. in theory one year you could pay about 24% on the gain while in the other year you may pay 0% or it might be 0% in either year or 24% in either year. it depends on what you'll have in the way of other income and deductions in each year. there are also potential changes in the tax laws that really makes it a guess.
