You can use Excel quickly everywhere.

With just your Microsoft Account, it's free.
https://office.live.com/start/Excel.aspx

(If you don't have one, you will be prompted to make one)

I was on a computer without Excel, but I really needed to run some numbers quickly.
Then I found that you can use it for free!

It doesn't matter if your calculations are small or complicated.
Excel works perfectly well for just calculating your groceries too.