When it starts and how often
The first heat usually comes at 6 to 15 months: earlier in small breeds, as late as 18 to 24 months in giants. After that, most dogs cycle roughly every 6 months, though anything from 4 to 12 months can be normal, and some breeds such as Basenjis cycle once a year.
The four stages
| Stage | Length | What you'll see |
|---|---|---|
| Proestrus | About 9 days (3 to 17) | Swollen vulva, bloody discharge, males interested but she refuses |
| Estrus | About 9 days (3 to 21) | Discharge lightens, she accepts males, ovulation; this is the fertile window |
| Diestrus | About 2 months | Pregnancy, or a hormonal phase that can cause false pregnancy |
| Anestrus | About 4 months | Rest between cycles |
Signs your dog is in heat
- Swollen vulva and spotting
- Licking the area more
- Peeing more often, marking
- Restlessness, clinginess, or grumpiness
- "Flagging": moving the tail aside when touched near the rump
Practical tips
Keep her on a lead and away from intact males for the full three to four weeks; males can scent her from a distance, and she can get pregnant on more than one day. Dog heat pants help indoors. If she does mate, see the dog pregnancy calculator for due dates. Talk to your vet about spaying timing, which varies by breed and size.
Frequently asked questions
Can a dog get pregnant on her first heat?
Yes, although she is not physically mature. Keep her away from intact males.
Do dogs go through menopause?
No. Cycles may get further apart with age, but unspayed dogs can keep cycling and conceiving for life.