you are not taxed on the cost basis. you're taxed on the gain which is sales price less tax basis. in addition, what tax bracket you are in will depend on whether the gain is short-term or long-term. short-term is treated like salary so that will push up your marginal tax bracket. There are special tax brackets for long-term gains depending on other income. there isn't one tax bracket based on your income. tax brackets are graduated
is sort of like steps. For example; taxable income from a to b is taxed at 10%, taxable income from b to c is at 12%, the next ranges are taxed at 22%, then 24%, etc. so at say $90K of taxable income a portion would be tax at 10% the next portion at 12% and the final portion at 22%. these are JUST EXAMPLES. also as noted long-term capital gains get a special rate that depends on your other income.