Free dog calculator
Dog Heat Cycle Calculator
This dog heat cycle calculator estimates where your female is in her current heat and when the next one is likely to start, using the cycle lengths in the Merck Veterinary Manual. Enter the first day you saw signs of heat.
- Cycle averages from the Merck Veterinary Manual
- This heat’s stages and the next one
- Free, no sign-up or email
Stage lengths vary a lot between dogs and between heats. The calculator shows averages; for breeding, ovulation timing by your vet is the only reliable way to find the fertile days.
How the heat cycle calculator works
Merck describes four phases. Proestrus, when she attracts males but won’t accept them, lasts about 9 days on average. Estrus, when she accepts breeding, also averages about 9 days. Diestrus follows for about 2 months if she isn’t pregnant, then anestrus, the resting phase, for 1 to 6 months.
The calculator places estrus right after an average proestrus, from about day 10 to day 18, and dates the next heat 7 months after this one started, the average interval Merck gives.
| Phase | Average | Normal range (Merck) |
|---|---|---|
| Proestrus | About 9 days | 2 days to 3 weeks |
| Estrus | About 9 days | 3 days to 3 weeks |
| Diestrus (not pregnant) | About 2 months | |
| Anestrus | 1 to 6 months | |
| Heat to next heat | 7 months | 4 to 13 months |
Keep a heat log
The calculator runs on averages, but your dog’s own history beats them after two or three cycles. Merck lists the signs a vet wants to hear about: vaginal discharge, swelling of the vulva and attraction to male dogs. Note each one with the date.
- The first sign you saw, and which one. This is the date to enter above.
- Whether discharge, swelling and male interest are still there.
- The day the signs stop. Proestrus plus estrus averages about 18 days in Merck’s figures.
- The date of the next first sign. After two cycles you have her real interval, and you can enter it instead of guessing.
Our guide to how often dachshunds go into heat covers what owners see at each stage.
Spay before or after the first heat? The dachshund study
Plenty of dachshund owners say their vet wants to wait until after the first heat to spay. In one r/Dachshund thread about a first heat, an owner whose vet advised just that got a reply pointing to a lower risk of back disease. There’s a dachshund-specific study behind that idea. In 2018, Dorn and Seath analyzed the Dachslife 2015 owner survey of 1,964 dachshunds and compared intervertebral disc herniation (IVDH) by neuter status in the 1,073 dogs aged 3 to 10.
| Group | IVDH per 1,000 dog-years | Risk vs. unspayed or intact |
|---|---|---|
| Females, not spayed | 54 | baseline |
| Females spayed before 12 months | 114 | 2.1 times |
| Females spayed after 12 months | 83 | 1.6 times |
| Males, intact | 59 | baseline |
| Males neutered before 12 months | 91 | 1.5 times |
| Males neutered after 12 months | 66 | 1.1 times (not significant) |
The authors concluded that neutering, especially before 12 months, raises the risk of IVDH in dachshunds. Two caveats: the disc problems were reported by owners, not taken from vet records, and a survey shows an association, not proof. Note that waiting for the first heat isn’t the same as waiting for 12 months: VCA puts the average first heat at about six months. Spay timing involves more than the back, so take this to your vet as one input, not the whole decision.
What changes the timing
Each dog’s rhythm
Most females cycle about twice a year, but Merck gives a normal interval of 4 to 13 months. Her own past dates are the best guide.
Big breeds
Some large breeds, such as Great Danes, normally cycle every 9 to 12 months.
Ovulation
Ovulation happens about 2 to 3 days after the LH peak, which you can’t see from outside. Behavior doesn’t always line up with the fertile period.
Spaying
Merck notes pregnancy can be prevented completely by spaying. Ask your vet about timing around her cycle.
Heat cycle questions
How long does a dog stay in heat?
Proestrus and estrus together average about 18 days, by Merck’s averages of about 9 days each. Either phase can be as short as a few days or as long as 3 weeks.
When does a dog have her first heat?
VCA Animal Hospitals puts puberty at about six months on average. Smaller breeds, dachshunds included, tend to cycle earlier, while large and giant breeds may not have a first heat until 18 months to 2 years. VCA also notes that first cycles are often irregular, so don’t read too much into the calculator’s dates until she’s had a couple.
How often do dogs go into heat?
Usually twice a year. Merck puts the average gap at 7 months, with 4 to 13 months still normal.
When is my dog most fertile?
During estrus, around ovulation, which Merck places 2 to 3 days after the LH peak. Because the peak isn’t visible, vets use serial progesterone or LH blood tests, usually every couple of days, to find it.
Sources
- Merck Veterinary Manual pet owner version, Management of Reproduction in Dogs: phase lengths, cycle interval, large breeds, ovulation timing (read October 2026).
- Merck Veterinary Manual, Breeding Management of Dogs and Cats: interestrous interval, estrus length, LH peak (read October 2026).
- VCA Animal Hospitals, Estrus Cycles in Dogs: age at first heat by breed size, irregular first cycles (read October 2026).
- Dorn M., Seath I.J., Neuter status as a risk factor for canine intervertebral disc herniation (IVDH) in dachshunds: a retrospective cohort study, Canine Genetics and Epidemiology, 2018: incidence and risk ratios by neuter status and age.