I'm with everyone else, it's so dependant on so many things.

I was/am overweight to begin with so I only put on about 8-9kg with both of my babies, and then by the time they were born, I actually weighed less than I did pre pregnancy (mind you that all came back on pretty quickly, lol!) This pg I was/am at my heaviest and I have already put on 5kg. I'm hoping to slow that down, and possibly even not put on too much more by eating a better diet and exercising gently. But I am very overweight.
My girlfriend was tiny before she had her bub, maybe a size 6-8, and by the time she had him, she'd gained 30+kg. Now, about 6 weeks after he was born, she's lost 20kg of that already. It's a very individual thing. Try not to worry too much. You can do what you have to once baby is here. Meanwhile enjoy your last few weeks of being pg!