Answer: Wolfram Alpha a ‘computational knowledge engine’

why ?

because you type in life expectancy for me at 33 and it gives you are rather precise 78.43 years.

then you type in your birthday + 78.43 years and you get

10:48.00 pm, Saturday, October 24th 2054 – which means I’ll miss Match of the Day

a page i might not bookmark because it also has a countdown timer on it