Does -0.50 plus -0.50 make -1.00?

Hi there. I've been wearing prescription glasses for almost a year now. It's only -0.50 for both eyes and have two pairs of glasses, I leave a spare cheap one in the car in case I forget mine. A little over a month ago, I was messing around and looked through my spare glasses with my glasses on and notices things were super clear. After that, I went and had my eyes checked again and the doc says he'll prescribe me at -0.75 so it won't be too strong on my eyes. Lately, I've been comparing the two, -0.75 and double -0.50, and still find the double -0.50 looks slightly clearer. Does this mean I can safely get -1.00 prescription? I need to get new lenses because mine are scratched up so I was thinking to ask to get -1.00. Think it's okay?