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Dog Heat Cycle Calculator

Predict your dog's next season and the stages of the heat cycle.

✔ Reviewed by a licensed veterinarianContent updated 18 Oct 2026Reviewed 18 Oct 2026Sources: Merck Veterinary Manual · Concannon P.W.
Dog Heat Cycle CalculatorFree · instant
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Quick answer. Most dogs come into heat about every 7 months, with a range of 4–12 months, and smaller breeds often cycle more often. Proestrus and estrus each last roughly 9 days. Enter the date the last heat started to estimate the next one, then track two or three cycles for your dog's own pattern.

How to use the dog heat cycle calculator

  1. Enter the first day of the last heat.
  2. Adjust the usual interval if you know it.
  3. Press Calculate.

Worked example

A dog whose last heat started on 1 September 2026 and who usually cycles every 7 months.

Start of last heat
2026-09-01
Usual interval (months)
7
Next heat ≈ 1 Apr 2027
Proestrus ends ≈
10 Apr 2027
Estrus ends ≈
19 Apr 2027

Cycle length varies between dogs and breeds; track 2–3 cycles for your dog's own pattern.

Example values are illustrative; this result is produced by the same calculator above.

How we calculate it

Interoestrous interval average ~7 months (range 4–12, smaller breeds more often); proestrus ≈ 9 days, oestrus ≈ 9 days

Sources: Merck Veterinary Manual · Concannon P.W.

Understanding your result

Most dogs come into heat roughly every 7 months, though the normal range is 4 to 12 months. Proestrus lasts about 9 days and estrus about 9 days.

Enter the first day of the last heat and your dog's usual interval. The tool estimates the start of the next heat and when each stage ends.

These are averages; individual dogs vary, so keep a record of real dates.

Common mistakes

  • Entering the end date instead of the start date of the last heat.
  • Assuming every cycle is the same length.
  • Relying on dates alone for breeding decisions; use a vet's tests for timing.

Good to know

  • No first heat by 2 years of age, a heat lasting longer than 4 weeks, or illness after a heat needs a vet.
  • Discharge with illness after a heat can indicate a serious womb infection and is urgent.
  • Ask your vet about the right time for spaying.

When to talk to your vet

  • No heat by 2 years of age
  • Heat lasting more than 4 weeks
  • Discharge with illness after a heat (possible pyometra — urgent)

Frequently asked questions

How often do dogs go into heat?

About every 7 months on average (range 4–12). Small breeds often cycle more often than giants.

How long does a dog stay in heat?

Proestrus and estrus together usually last about 2–3 weeks.

When is a dog fertile?

During estrus; timing varies, so breeders use progesterone tests with their vet.

Is the next-heat date exact?

No. Cycle length varies between dogs and breeds, so treat the date as an estimate and track two or three cycles to learn your dog's own pattern.

When should I talk to a vet about heat cycles?

Talk to your vet if there is no heat by 2 years of age, if a heat lasts more than 4 weeks, or if discharge and illness follow a heat, which can be urgent.

What are proestrus and estrus?

Proestrus is the first stage, about 9 days, with swelling and bloody discharge. Estrus follows for about 9 days; it is when a female accepts mating and can conceive.

Reviewed by a licensed veterinarian
Last reviewed 18 Oct 2026 · How we review

Sources

  1. Merck Veterinary Manual — Management of Reproduction in Dogs (pet owner version)
  2. Concannon P.W. (2011) Reproductive cycles of the domestic bitch. Animal Reproduction Science 124:200–210

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Estimates only. Every pet is different — confirm with your veterinarian. If your pet may have eaten something harmful, contact your vet or an animal poison helpline now.