My wife and I are salaried and pay most of our taxes in our paychecks. If we realize capital gains early in the year, can I just submit a payment to the IRS to cover the expected taxes? The last couple of years our withholding has been short, even after eliminating exemptions and adding a fixed amount to be taken out each pay period (new withholding system not working great for us!). So, I know any capital gains could risk us being short and getting a penalty. I'd like to just send in 20% of the gains and cover my bets, but don't want to complete estimated tax forms if I don't have to. Can this be done?