How old does a toy puppy have to be to go in heat?

I don't want her getting pregnant before I get her spayed. Christmas is expensive and she just turned six months old. I'm hoping to get her spayed in January. I never let her outside without me because she's the cutest and tiniest little toy fox terrier there is! I am worried about going for walks and encountering a male dog on the loose!|||around 6 months. same for any dog.|||You'll stillhave time, most dogs hit a heat around 7-8 mos. If you start noticing that her vulva starts to swell and bleed, don't take her out... she won't be accepting males until near the middle of her cycle (a cycle runs for about 3 weeks), but to be on the same side if you do notice her go into heat before you get her spayed, just don't take her out.|||Dogs go into their first heat cycle anywhere from 6 months to 12 months. Since you dog is a toy puppy then you should have no problem picking her up if a male comes around if she goes into heat. Besides that you should know when she goes into heat before she will be receptive to a male. Female dogs are usually receptive to the males after the "dripping stops", and usually only for a time period of up to 14 days after the bleeding stops. This would be the time to be very concerned if you do not want her to have pups. Other thatn that you should be fine till January.