Ther is no fix thing but around 10 kg on average normal weight gain.. if you eat healthy and go little bit of exercise then it will be fine

Any gain between 7-20 kgs is considered normal as per body build. Overweight women are advised controlled gain up-to 10kgs maybe while avwrga build women end up gaining even up-to 15. I'd suggest you eat healthy and give in to junk only when craving big time. Weight gain is better off when controlled since eating for two is no longer the norm.