Track your female dog's estrus cycle, estimate fertile days, and predict the next heat.
Proestrus (days 1–9): bleeding begins, not yet receptive. Estrus (days 9–14): fertile window, receptive to mating. Diestrus: pregnancy or false pregnancy phase. Anestrus: rest period. Most dogs cycle twice yearly. Toy breeds may cycle 3–4x/year; large breeds once yearly.