Dog Heat Cycle Calculator

Where your dog is in her heat cycle, her likely fertile window, when it ends and when the next heats are due.

A dog's heat lasts about 2–3 weeks. Proestrus (bleeding, not yet receptive) runs about 9 days, then estrus about 9 days, when she is fertile; most dogs ovulate around days 10–14. Heats recur about every 6 months, less often in giant breeds.

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How to use it

  1. Enter the first day you saw swelling or bloody discharge.
  2. Pick her size, or enter her usual months between heats.
  3. Read today's phase, the fertile window and the next heat dates.

What you enter

What you get

Formula

Proestrus ≈ days 1–9 | Estrus ≈ days 10–18 | Fertile window ≈ days 10–15 | Next heat ≈ start + interval (months × 30.44 days)

Worked example

Input: Heat started 20 days ago, medium-sized dog

Result: Late estrus; next heat in about 6 months

Keep her away from intact males for a few more days.

Questions

How long is a dog in heat?

Usually 2–4 weeks from the first sign of swelling or bleeding, averaging about 18–21 days.

When is a female dog most fertile?

During estrus, typically days 10–14 after bleeding starts, when discharge lightens and she accepts the male. Ovulation timing varies widely, so breeders confirm it with blood progesterone tests.

How often do dogs go into heat?

Most every 5–7 months, about twice a year. Small breeds can cycle 3 times a year; giant breeds may cycle every 12–18 months.

At what age does a dog have her first heat?

Around 6 months in small breeds and up to 18–24 months in giant breeds.

Can a dog get pregnant when not bleeding?

Yes. Bleeding often lessens or stops during estrus, which is exactly when she is most fertile.

Limitations

References

Related reading

More Pet Care

All free tools · By Dr. Zubair Khalid, DVM, MS, PhD.