The way I understand it the price you bought at plus $250k, after that you pay capital gains.
IRS tax code 121
$500K for married couples. The seller pays long term capital gains. The rate varies on income. The rates are 0, 15 and 20%. I wouldn't think many single people would be eligble for the 0 rate. It is probably a bit easier for married couple to pull it off if they own the house outright or have low mortgage payments..