I assume by calories you mean kilocalories in which case you are probably looking around 1000 KJ (kilojoules) for two slices of toast with Nutella. That's around 239 (kilo)calories.
Wheat bread's about 75 calories a slice, so 150 for just the bread. I don't know about you, but I put it on thick—maybe a serving-and-a-half per slice, which according to the Nutella website is 570 calories. So 720 total. Not 1,000, but closer to it than 239.
A serving size is 2Tbsp, which is what I put on a serving size of bread (1 slice) when I'm paying attention to how much I'm putting on. Like I said, though, I tend to slather it on (mainly because Nutella is so damn good)—so I'm really getting 1.5-2 servings of Nutella per slice.
Two slices—75kcal * 2—and a hunk of Nutella—190kcal * 3—is way the hell more calories than I should be eating as a snack (720kcal). Veeeery easy to go overboard.
