Just out of curiosity, I happened to be thinking about how much I've played so far this year and it's pretty worrying, frankly.
But. Right now we are almost a 3rd of the way into 2013, and just over 100 days in as well. Which makes rough calculations really simple as to how much you've played so far.
Because I don't have an adventurers log to check my gametime, (I don't even know if I want to check if I did.) I can only give rough estimates.
So. 102 days of 2013, and I've gained 97m total xp.
I could type out some boring calculations and such but I'll just sum it up.
That's 950k Average xp/day in F2P, whilst the vast majority of that is in faster skills such as Fm/Cook, it's still a lot of hours put in.
More rough calcs;
~75m Cook xp = ~550 hours
~10m Fm xp = ~70 hours
~4m Wc xp = ~150 hours (Mainly because I cut 18k yews for this instead of willows.)
~4m Rc xp = ~120 hours
Then random stats and/or skillwars which I'll guess at around 50 hours.
So whilst that is in no way exact, I've played roughly 940 hours so far in 2013.
(Just over 9hours/day, which when considering I didn't log on at all for maybe 10 days out of those 102 is pretty bad.)
Also means I've averaged about 100k xp/hour which is kind of cool.
So, if you want to work this out yourself, I think there's something on Runetrack that lets you know xp you've gained since X point in time, so just use that - assuming you've been playing on the one account. And then work out roughly xp/hour of the methods you did and the hours spent on that xp/hour to get to game time played + xp gained on average and such.
Or if you know what Gametime you had at the start of 2013, you can use that with xp gained to speed it up.