TimeSpan don't support years so how do I deal with it? Is there could be smarter solution? explain:

from start day till now I've got 7.7 mb size, how long it will be to make it 10 gb size

open System

let dd = (DateTime.Now - DateTime.Parse("12/09/2012")).Days
let oneday = 7.7 / Convert.ToDouble(dd)

let in10gb = Convert.ToInt32( Math.Round (10.0 * 1024.0 / oneday) )
let years = Convert.ToInt32( Math.Round (float in10gb / 365.0) )
let mutable months = Convert.ToInt32( Math.Round (float (in10gb - years * 365) / 30.0) )
let days = 
    let d = in10gb - years * 365 - months * 30
    if d &gt; 0 then d else month = month - 1; (30 - d)

printf "%d years %d months %d days" years months days
Console.ReadKey() |&gt; ignore


Also / 30.0 for months is dirty hack here... I'm not sure how to avoid it in easy way.
I would propose an alternative method of calculating your time, using seconds and DateTimes:

open System

let startDate = DateTime.Parse ("2012-09-12")
let now = DateTime.Now;
let currentRuntime = (now - startDate).TotalSeconds
let timePerGig = currentRuntime / 7.7;
let tenDate = startDate + TimeSpan.FromSeconds (10.0 * timePerGig);


With that done, you can do whatever you like to represent the final date relative to the current date.

An overly simplistic example is as follows:

printf "%d years %d months %d days" (finalDate.Year - now.Year) (finalDate.Month - now.Month) (finalDate.Day - now.Day)


Of course, you would have to account for roll-over for days and months in any final piece of code, but it illustrates how you could pull the date parts back out.