Seeding~ Every spring I am asked when should I seed my lawn? This is something you will have to way out based upon a few factors. March is the ideal time for us to put down our crabgrass preemergent to protect your lawn against summer annual grassy weeds.  The residual of this will prevent new seed growth for a couple of months. Then you are into hotter weather making it more stressful on new grass plants. So there is a trade off.  

Seed in the spring and gamble with the crabgrass. Which can be treated later after it has come up but is not cheap to do so, or have the preemergent applied in the spring and wait until fall to seed.  If you have a  decent turf stand and have had problems with crabgrass I would treat for it and wait until fall to seed. Then again if you have a very thin lawn to the point you can see a lot of soil, I would not use spring preemergent  and seed.