Dog Heat Cycle Calculator Next Heat, Fertile Days & Season Calendar
Find out which stage of her cycle your dog is in today, when her next heat will start, her likely fertile days and a 12-month season calendar. You can also predict a puppy’s first heat from her birth date.
By Manzoor Ahmad · Updated October 18, 2026
Enter the first day you noticed bleeding or swelling in her last heat.
Personalize with her past heats (more accurate)
Today
Next heat expected
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Enter a date to see her cycle.
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Stages of her current cycle
12-month heat calendar
Outlined day = todayYour plan
How often do dogs go into heat?
Most female dogs go into heat about every 6 to 7 months, roughly twice a year. A normal interval ranges from about 4 to 12 months. Small breeds tend to cycle more often, giant breeds less often, and a few breeds such as the Basenji cycle only once a year. Each heat lasts about 2 to 3 weeks: about 9 days of proestrus (bleeding, swelling, no mating) followed by about 9 days of estrus, when she accepts a male and can get pregnant. Ovulation happens on average around day 12 after bleeding starts, but anywhere from day 5 to day 27 is possible.
How to use the dog heat cycle calculator
- Choose a mode. Use “She’s had a heat” if you know when her last season started. Use “Puppy’s first heat” for a young dog that hasn’t cycled yet.
- Enter day 1 of her last heat. That’s the first day you saw bloody discharge or a swollen vulva, not the day she accepted a male.
- Add past heats if you have them. Two or three start dates let the tool calculate her interval and show how regular she is.
- Pick your goal. The plan changes depending on whether you want to avoid pregnancy, plan a breeding or schedule a spay. Save every date with “Add to calendar”.
The 4 stages of a dog’s heat cycle
A dog’s reproductive (estrous) cycle has four stages. Only the first two count as being “in heat”, but the calculator maps all four so you always know where she is.
| Stage | Typical length | What you’ll notice | Can she get pregnant? |
|---|---|---|---|
| Proestrus | ~9 days (3–17) | Swollen vulva, bloody discharge, licking, males interested but she refuses them | Usually not yet, but sperm can survive until she ovulates |
| Estrus | ~9 days (3–21) | Discharge lightens to straw-pink, she “flags” her tail and stands for males | Yes: this is the fertile stage |
| Diestrus | ~60 days | Swelling and discharge fade. She refuses males. False pregnancy signs are possible. | No. She is either pregnant or her hormones mimic pregnancy. |
| Anestrus | ~3–5 months | No signs. This is the reproductive “rest” period. | No |
Next heat = last heat day 1 + her interval (default 6–7 months by size)
Personal interval = average gap between her past heat start dates
Likely fertile days = day 10–16 of heat (ovulation averages day 12, range 5–27)
When does a dog have her first heat?
Puberty depends mainly on size. Small dogs mature early, while giant breeds may not cycle until they’re nearly two. The “Puppy’s first heat” mode uses these ranges.
| Breed size | Typical first heat | Typical interval after |
|---|
If she hasn’t had a heat by about 24 months, ask your vet. She may have had a “silent heat” with few visible signs, or there may be a hormonal or developmental cause worth checking.
Signs your dog is in heat
Physical signs
A swollen, softer vulva, bloody or pink discharge, frequent licking of the area, and more frequent urination as she “marks” for males.
Behavior changes
Clinginess or restlessness, nesting, mounting, a lower appetite, and tail “flagging” to one side when touched near the base of the tail during estrus.
Male attention
Intact males may gather, howl or try to escape to reach her from a long way off. This is often the first sign owners notice.
Best time to breed a dog: why a calendar isn’t enough
Counting days is a starting point, but ovulation can happen anywhere from day 5 to day 27 after proestrus begins, so a “breed on day 11 and 13” rule misses many females. Breeders use serum progesterone testing, starting about day 5–6 of heat and repeating every 2–3 days, to pinpoint ovulation.
| Progesterone level | What it means | What to do |
|---|---|---|
| Under 2 ng/mL | Baseline, before the LH surge | Retest in 2–3 days |
| About 2–3 ng/mL | LH surge, the “day 0” of pregnancy timing | Ovulation expected in about 2 days |
| About 4–10 ng/mL | Ovulation day | Eggs need 2–3 days to mature. Plan breedings over the next few days. |
| Over 5 ng/mL, rising | Post-ovulation fertile period | Breed. Eggs remain viable for roughly 4–6 days after ovulation. |
Once she’s bred, switch to the Dog Pregnancy Calculator. Entering the LH surge date there narrows her whelping date to a 3-day window.
Worked example: Luna, a medium-size dog
- Last heat started: 40 days ago, so today she is on day 41, in diestrus.
- Default interval: about 7 months (213 days) for a medium dog, so her next heat is expected about 173 days from now, give or take about 3 weeks.
- Next fertile window: days 10–16 of that heat. Keep her away from intact males from day 1 to about day 21.
- Spay timing: many vets prefer to spay about 3 months after a heat begins, once diestrus hormones settle. For Luna that’s about 7 weeks from today.
These are the calculator’s default values, so you can check every number above.
Irregular heats: when to call the vet
Talk to your vet if your dog:
- Has thick, smelly, pus-like discharge, drinks a lot, vomits or seems lethargic 2–8 weeks after a heat. These can be signs of pyometra, a life-threatening uterine infection.
- Stays in heat (bleeding or attracting males) for more than about 4 weeks
- Cycles more often than every 4 months, or goes more than 12–18 months without a heat (except once-a-year breeds)
- Has not had a first heat by about 24 months of age
- Shows a “split heat” (signs that stop and restart within weeks) more than once
- Has heavy bleeding, or bleeding outside a heat
A pharmacist’s tips for caring for a dog in heat
- Don’t give human pain relievers for heat discomfort. Ibuprofen, naproxen and acetaminophen can be toxic to dogs. Ask your vet if she seems sore or restless.
- Avoid human “period” products and scented wipes. Use washable dog heat pants or diapers and change them often to prevent skin irritation and urinary infections.
- Don’t rely on over-the-counter “heat suppressant” sprays or supplements. Masking sprays don’t prevent pregnancy, and no supplement reliably stops a cycle.
- Hormonal “mismating” injections or tablets are prescription-only. They carry real risks. Talk to your vet the same day if an unplanned mating happens.
- Keep her on a leash and supervised outdoors from the first sign of swelling until about 3 weeks later. Fences rarely stop a determined male.
Related dog calculators
Her heat cycle connects to every other stage of her reproductive life. These tools pick up where this one leaves off:
Dog heat cycle FAQs
About 2 to 3 weeks. Proestrus averages about 9 days and estrus about 9 days, but each can range from roughly 3 to 21 days. Keep her away from intact males from the first sign of swelling until about 3 weeks later.
Most dogs cycle every 6 to 7 months, about twice a year. Small breeds may cycle up to three times a year, giant breeds every 9 to 12 months, and Basenjis once a year.
Add her usual interval to the first day of her last heat. If she usually cycles every 6 months and her last heat started on March 1, expect the next one around September 1. Tracking two or three past heats makes the estimate much more accurate.
Usually during estrus, often around days 10 to 16 after bleeding starts. Ovulation averages day 12 but can happen anywhere from day 5 to day 27. Progesterone blood tests are the only reliable way to time breeding.
Yes. Bleeding often fades or turns straw-colored during estrus, which is when she’s most fertile. A lighter discharge doesn’t mean the risk has passed.
Usually between 6 and 24 months. Toy and small breeds often start at 6 to 12 months, medium and large breeds at 7 to 15 months, and giant breeds at 12 to 24 months.
No. Dogs don’t go through menopause. Older females keep cycling, though intervals may lengthen and signs may be milder. Senior intact females have a higher risk of pyometra, so discuss spaying with your vet.
Many vets prefer to wait about 2 to 3 months after a heat ends, once hormone levels and blood flow to the reproductive tract settle. Timing varies by vet and dog, so confirm with your veterinarian.
A silent heat is a cycle with few or no visible signs. She still ovulates and can get pregnant. It’s more common in young dogs and is one reason first heats can seem late.
In a split heat, proestrus signs start, stop without ovulation, then restart a few weeks later. It’s most common in young females and usually resolves, but repeated split heats are worth discussing with your vet.
It’s a good planning estimate. With only a default interval, expect the next heat within about 3 weeks of the predicted date. Adding her own past dates usually tightens that. Fertile days are averages, and only progesterone testing confirms ovulation.
Spaying is the only permanent, reliable way. Prescription hormonal options exist in some countries but carry health risks and need a vet’s supervision. Sprays and supplements don’t stop a cycle or prevent pregnancy.
Manzoor Ahmad
Pharmacist & health writer · 13+ years of web development and SEO experience
Manzoor is a pharmacist with more than nine years of experience writing evidence-based health and supplement content. He builds every dexocalc pet calculator from primary veterinary references. The stage lengths, ovulation timing and progesterone values in this tool follow canine reproduction research presented at WSAVA World Congresses and the Merck Veterinary Manual. This calculator supports planning. It does not replace your veterinarian.
Sources
- Recent Advances in Canine Female Reproduction. WSAVA World Congress Proceedings, 2006 (VIN).
- Concannon PW. Understanding and Monitoring Canine Pregnancy. WSAVA World Congress Proceedings, 2005 (VIN).
- Concannon PW, Verstegen J. Pregnancy Management in Dogs and Cats. WSAVA World Congress Proceedings, 2004 (VIN).
- Davidson AP. Whelping and Queening in Dogs and Cats. Merck Veterinary Manual (revised June 2025).
Disclaimer: This dog heat cycle calculator gives educational estimates based on published canine averages. Individual dogs vary widely, and a calendar can’t confirm ovulation or guarantee that pregnancy won’t happen. Use progesterone testing with your veterinarian for breeding, and contact a vet about any abnormal discharge, prolonged heat or signs of illness.