Congrats on finishing your top! I don't like to do much math, and as a long armer, 'friendly' (read: waving at you!) borders can be challenging! I found this method in Quiltmaker a few yrs ago and it has stood me in good stead. It is the same as measuring thru the center, but no math.

Fold your quilt in half and lay it on a flat surface. Lay your borders (cut both sides at once) along the fold in the middle. Smooth the quilt and borders, pinning as needed. Trim the borders on each end. The theory is that both borders are the same and will aid in keeping it sq and flat. If your ends are not even, you will have to ease or adjust on that seam. Better a bit of fullness inside the quilt than a large wavy border.

This is just ONE method, and just because it works for ME, does not mean it has to work for YOU. Try one method and if that does not suit, next quilt, try a different one.

Lots of good advice here! Can't wait to see your quilt.

Help with first quilt - ok, this is probably a really dumb question, but I am stuck on putting the last two borders on my quilt top. I have sewn the side borders and had some slight puckering/pleats in my seam. I had to rip out a couple of times, but I think after I quilt it hopefully it won't be too bad. My borders are attached to long strips of sashing. The pattern calls for me to put a 5.5" x 5.5" block at the ends of each of the top and bottom borders. When I measure for these borders, do I measure to the end of the seams from the top and bottom of the quilt? In other words, I ignore the already sewn on side borders? I added 1/2" to the width of each of my side borders. So after I sew these last two borders on, do I just go around and make sure that it is square and trim off the extra width? I know I have so much to learn with quilting. I really enjoy sewing, but honestly I'm getting a little stressed over my first quilt. Thank you all for your helpful advise!

I like to square mine up at each stage.