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Dog Heat Cycle Calculator Guide
Tracking your dog's heat cycle helps you plan for breeding or simply be ready for the next season. Enter the start of the last heat and this calculator predicts the next cycle and the fertile window within a heat.
Most dogs cycle about every 6 months (small and medium breeds), while large breeds run 7–8 months and giant breeds roughly once a year. The fertile window falls around days 9–15 of a heat, with ovulation near day 11–14.
When Will My Dog Be in Heat?
Add your dog's typical cycle interval to the start of the last heat to estimate the next one. Within each heat, bleeding starts in proestrus, and the fertile estrus phase (when she'll accept a mate) usually begins around day 9 and lasts through about day 15.
Stages of the Heat Cycle
| Stage | Days | What Happens |
|---|---|---|
| Proestrus | Day 1–9 | Swelling and bloody discharge; not yet fertile |
| Estrus | Day 9–15 | Fertile window; ovulation around day 11–14 |
| Diestrus | Day 15–60 | Cycle winds down (or pregnancy begins) |
| Anestrus | ~4–7 months | Resting phase until the next cycle |
Worked Example
Last heat started January 1 for a medium breed (6-month cycle): next heat ≈ July 1. The fertile window in a heat runs roughly January 9–15.
Tips
- Progesterone testing at the vet pinpoints ovulation far more precisely than day-counting for planned breeding.
- Cycles are irregular in young dogs and settle after the first year or two.
- Log each cycle's start to sharpen future predictions.
Planning a litter? Continue with our Dog Pregnancy Calculator once bred, and size the pups with the Puppy Size Calculator.
Frequently Asked Questions
When will my dog go into heat?
Add your dog's cycle interval — about 6 months for most breeds — to the start of the last heat to estimate the next one.
How long is a dog's heat cycle?
The visible heat lasts about 2 to 3 weeks, within a full cycle that repeats roughly every 6 months.
What are the fertile days in a dog's heat cycle?
The fertile window is usually days 9 to 15 of the heat, with ovulation around day 11 to 14.
How often do dogs go into heat?
About twice a year for small and medium breeds, less often for large and giant breeds.
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