I pay in about 6K every year to Federal and another 600 to state. I keep thinking I must be missing things but I always come up with the same lists every year.
Do make sure when you figure your hours that you worked, you add all those hours you've put in at home doing dc-related activities. Cleaning dc rooms, planning meals, being here on this forum, taking on-line classes at home, prepping curriculum or materials, working on taxes, rewriting your policies, meeting with potential clients, etc., etc. It will up your T/S ratio and help a bit.
Another thought...the first several years I worked I made zilch because I was just getting started. I was so excited. But all those years are coming back to haunt me because I won't get much at all in social security. Certainly not enough to retire at 65.