help calculating how many days take a number to double (or triple)

Hi,
I'm working for a regional newspaper in Spain and my Excel knowledge is a bit limited.

We have an excel with Coronavirus daily cases for several geographic divisions (regions, countries...)
It follows this structure (I apologize, but the button to attach a file doesn't allow me to upload):
Place 8/3/20 9/3/20 10/3/20
Andalucía 35 54 71
Aragón 13 13 38
Asturias 7 7 28
Baleares 8 11 13

Is there a formula that can help us to discover how long does it take to [double|triple|etc] the number of cases (a growth rate)?

So, as in the small example above, in the line "Andalucía" first number of cases is "35". We want to see how many days it takes to double (8/3/20 is 35; double is 70 >> the first day that there is a number that is equal or bigger than the double is 10/3/20, so the result is 2 (days))

Or in the line "Asturias", if we want to see how long does it takes to triple, from the first day "7" it takes 2 days to do it.

I don't know if my explanation is clear. Sorry for my English.

Also, I don't know if our approach is correct.
I see in here (https://ourworldindata.org/coronavirus) that they do the calculation from the present day backwards.

Any help will be welcome.

Thanks in advance.

Thank you, Richard
Yes, unfortunately we 'll need to keep updating the statistics for a long time.

Your reply is exactly what we need, according to what the editor is asking for. More than a percentage number, that could be more abstract, better a period of time in which the figures multiply (x2, x3...)

Maybe the only thing we can play with is calculating it backwards: if today the number is, i.e., 568, how many days has take to FACTOR (double, triple).
I'm trying to modify your formula to achieve that, but I'm not managing to do it. I'll keep trying.

Thank you again, Richard
This is very helpful. And I realize that I have to learn Excel seriously