Weight gain calorie tool

I've been reviewing the weight gain advice on here, and I tried to use the weight gain tool to work out my calorie requirements to gain a pound a week.  I currently weigh about 46kg, but when I try to put this in as my current weight it says that it isn't a "valid weight" so won't give me a calorie target.  Can anyone help - sorry am probably just putting something in wrong - technology is not my strong point!

Did you make sure to click the button to change to metric measurements?  It is set to lbs. so it won't accept 46 as a start weight.

mine's the same, I have it set to kilograms and it won't accept my weight, or anything under 50. I didn't bother using the calorie tool anyway though, there are plenty of sites which will calculate your bmr, and with weight gain you can just 'follow your progress' too.