It is more like 500 calories.

But yep, like N2L suggested, you can calculate it online. Basically you should be on around 2000 calories a day to maintain weight, plus your 500 for pregnancy.

Seriously though, it is more about listening to your body and eating as and when it demands, and eating healthy and nutritious food. Please don't get stuck flitting away your pregnancy worried about counting calories!
There is nothing that says you will put n weight either, BTW, I didn't put on any with either pregnancy; the healthy weight gain is around 11kg, most of which you will lose immediately post partum. Fat stores during pregnancy and breastfeeding are a physiological norm and your body needs them, so don't go overboard.