When is my jack russel going to be in heat?

Going into heat every 6 months is just based on the average. My mini doxie went into heat at 10 months then again at 19. A dog can go into heat 1-3 times a year. Also consider that she may sometimes have a silent heat which is very hard to spot and usually the only way you would know is when a male dog seems interested. You can not always predict when your dog will go into heat, it may or may not even be regular. A dog can go into heat from ever 4 months to every 14 months easily.