I'm trying to solve a math question. AIChatting.net is using 4o-mini and gives me answers that aren't logical and DeepAI.org gets caught in a loop adding up the number of days in all the months of the year. Math mode is locked behind a subscription.

I was born in the USA on July 2, 1986. I moved to Spain on September 17th, 2017. Today is June 28th, 2025. What percentage of my life have I lived in Spain? And on what date will I have lived 20% of my life here?

It should be a simple copy and paste job for anyone with a subscription to one of the decent models.

excel can easily calculate days between dates.

you've lived 2842 days in spain out of 14242 days of your life. that's 19.95506%.

to find 20%, use:
(2842 + x)/(14242 + x) = 0.2

on july 7, you'll have lived 20% of your life in spain.