Dog Heat Cycle Calculator

Usually twice yearly (every 6 months), but ranges 4–12 months normal. Smaller breeds more frequent. Larger breeds less frequent. Nursing, illness can delay cycles.

During estrus (proestrus day 7–10 typically). Fertile window 48 hrs around LH surge (behavioral: standing to mate). Sperm live 7 days in female tract; egg 24–48 hours.

Swollen vulva, bloody discharge, increased urination, behavioral changes (restlessness, nervousness). Some breeds discharge less visible. Smell test: males attracted from distance.