If half your SS plus your other income is more than $32,000, then part of your SS benefit becomes taxable. So you will start to have "taxable income" at only $7000 of gains. But, you have a standard deduction of $29,200, so even though your benefit is partly taxable, you won't owe tax until your total taxable income is more than your standard deduction.
Then, short term capital gains are taxed along with ordinary income, but long term capital gains are tax-free unless your total taxable income rises above $123,000 (including the standard deduction).
So it's a complicated moving target. You could potentially have a long term capital gain of up to $80,000 and not pay capital gains tax, but you would still pay some tax on the taxable portion of your SS benefit. The tax caster app is probably the best way to play around with numbers.
