The gains you incurred this year are not taxed until next year, tho it's possible you would be obliged to pay some estimated tax. But that has nothing to do w/April 15. If you realized gains last year and plowed it back into other stock, expecting to cash out only to pay your tax on 4/15, then there could be some effect. Of course, capital gains are taxed at a pretty low rate to begin with, and the rules are so complicated there is often a way to plan how to avoid tax on realized gains legally.
mbs