For a woman finding a pair of jeans that fit is almost impossible. Especially if you have a curvy body. I am talking a smaller waist, bigger hips and well, junk in your trunk. What usually happens for me is that I can get them to fit everywhere but in the waist. I hate when my jeans gap in the waist at the back. I swear I could fit a pillow down there. If you have a smaller waist like I do, this is a huge problem for you, specifically when it comes to jeans. I have the hardest problem finding jeans that fit, not only in length but more importantly in the waist. So I find jeans that primarily fit in the hips, rear, thighs, and are long enough for my 5'9 frame. So to fix the gap at the back of your jeans, there is a simple fix and I will show you how to do this.
First lay your jeans out flat on the table and look at the waist.
Now turn them inside out and match the middle belt loop in the seam of the seat to the belt loop on the right.
Pin the belt loops together so they don't slip around. Now I know that my waist is about three inches too big. I know because if you pull the waist tight on the side when you try them on you can figure out how much excess is there. It is usually about three inches for me. So, I am going to place my dart in the back of the waist about 1 and 1/2 inches on each side for a total of three inches. So I measure and then mark with my marker where I need to begin my dart.
Lay the ruler from the top of waist band which is 1 1/2 inches in and place it diagonally to the top of the pocket seam on the jeans. It needs to taper slowly otherwise it will pucker. See photo...
You are ready to sew. Make sure you use a couple pins so the seams remain straight and flush. Sew a straight line. Do the other side of the belt loops the same way.
Cut away the excess fabric and zig zag stitch the cut seam so it doesn't fray.
When you are finished your new tappered waist should look like the photo below.
And the finished waist should look like the photo below.
And finally a closeup of me with no gapping and when I sit my underwear not showing, is just priceless.