TBF, I sent a little extra in for my 4th qtr estimate. When I file my usual extension in April, because I expect to own more, not less. Also, if I miss my total amount by more than 10% (15% this year because of the IRS' mercy - big whoop!), then I owe the failure to file penalty...Started mine yesterday and looks like we'll thankfully be staying about where we were last year.