Me too. I've learned that I end up wasting alot less fabric this way and alot less frustration when they don't come out to the right size. I always do it bigger and then square it up using the center line as a guide to make sure it even on both sides.

Quilt In A Days triangle square up ruler is a must have for me.
After demo at my quilt guild many have bought this ruler.
It saves so much time and effort and is such a simple way to square up. It amazes me that everyone dosnt have one.
One cut square up for perfect triangles.

I round up and trim afterwards using a new ruler that I bought called a BLOC-LOC. It has a groove for the seam line so it doesn't slip. I really like it.

This square up ruler is one of the best tools/rulers I have.

I finally bought one of these and now never have any problems, it is well worth the $ I spent...

I do this as well, it makes squaring up do much easier and more accuate.

One of the most important things to think about in trimming the HST, is to be sure the 45 degree line on your ruler is on the diagonal seam line. Also, if you have a Boston block, watch out for the other point. Make sure there is seam allowance enough so you don't lose that point. I made a quilt last year and put the ruler into the corner to trim and lost all my points on the Boston blocks.

Thank you for this link! I will have to buy one of those rulers.

Thats what's do, too. You can always trim off, but if you're too small, it's hard to manage it.