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.

Please keep in mind:
This is an online tool, not as fast as the real program!