Dog heat cycle calculator
Dogs normally come into heat every 4 to 13 months, with 7 months the average. So a dog whose last heat started in January is most likely to come in again around August, and anywhere from May to the following February is still normal.
If you know the date of the heat before the last one, the calculator uses your own dog's gap instead of the average, which is a far better guide.
- months between heats, 7 on average
- 4 to 13months between heats, 7 on average
- average length of each visible stage
- 9 daysaverage length of each visible stage
- predicted ahead, with the range around each
- 3 cyclespredicted ahead, with the range around each
Heat cycle calculator
Give this and we use your own dog's gap instead of the average.
Merck puts the normal gap at 4 to 13 months, with 7 the average.
Next heat most likely around
May 11, 2027
Normal range: Feb 9, 2027 to Nov 10, 2027.
Based on the 7 month average, because we have only one date.
Estimate only. For health questions, ask your vet.
| Cycle | Most likely | Could start as early as | Or as late as |
|---|---|---|---|
| Next heat | May 11, 2027 | Feb 9, 2027 | Nov 10, 2027 |
| Next heat plus 1 | Dec 10, 2027 | Jun 11, 2027 | Dec 9, 2028 |
| Next heat plus 2 | Jul 10, 2028 | Oct 10, 2027 | Jan 9, 2030 |
Scroll the table sideways to see every column.
| Stage | Average | Range |
|---|---|---|
| Proestrus, the bleeding starts | 9 days | 3 days to 21 days |
| Estrus, she can conceive | 9 days | 3 days to 21 days |
Scroll the table sideways to see every column.
In short
Key takeaways
- The published gap between heats is 4 to 13 months, averaging 7. That range is wide, and the calculator shows it rather than hiding it.
- Two dates beat one. Your own dog gap predicts better than any average.
- Proestrus and estrus each average 9 days, with a range of 3 days to 3 weeks.
- This is not a breeding-timing tool. Timing a mating needs progesterone testing by a vet.
- This is not birth control either. The range is far too wide to plan around.
The cycle
The stages of a heat
| Stage | What you see | Average | Range |
|---|---|---|---|
| Proestrus | Swelling and a bloody discharge. Males are interested, she is not. | 9 days | 3 days to 3 weeks |
| Estrus | She accepts the male. This is when she can conceive. | 9 days | 3 days to 3 weeks |
Merck: "Proestrus lasts from 3 days to 3 weeks, with 9 days average." and "Estrus lasts 3 days to 3 weeks, with an average of 9 days."
Scroll the table sideways to see every column.
Accuracy
Why your own dog's gap matters more
The 4 to 13 month range describes dogs in general. An individual dog is usually far more regular than that: a dog that went 8 months between her last two heats will probably go close to 8 months again, not 4 and not 13.
That is why the calculator asks for the heat before the last one. With two dates it measures the gap instead of assuming it. We still show the published 4 to 13 month range around the prediction, because one measured gap is a single observation rather than a pattern.
Young dogs are the exception. The first few cycles after the first heat are often irregular, and a gap measured across them is less useful than it will be later.
2 dates
turn a nine-month range into a real prediction
Limits
What this tool is not for
It is not a breeding-timing tool. Knowing roughly which month a heat will start tells you nothing about which days inside that heat a dog is fertile. That requires progesterone testing during the heat, done by a vet, and getting it wrong wastes a cycle.
It is not birth control. A prediction with a nine-month range around it cannot be used to decide when it is safe to let an intact dog off lead. If you want to avoid a litter, that is a conversation to have with your vet.
And it is not a health check. If your dog's cycle has changed, stopped, or looks unusual, that is worth a vet appointment rather than a calculation.
FAQ
Questions people ask
- How often do dogs go into heat?
- The Merck Veterinary Manual puts the gap between heats at 4 to 13 months, with 7 months the average. That means roughly twice a year for most dogs, but a dog on a 10 month cycle is still perfectly normal.
- How long does a dog stay in heat?
- Proestrus, when the bleeding starts, averages 9 days and can run from 3 days to 3 weeks. Estrus, when she can conceive, averages another 9 days with the same range. So the visible part of a heat is around 18 days on average, and can be anywhere from under a week to six weeks.
- How accurate is predicting the next heat?
- Only as accurate as the gap you feed it. Using the published 7 month average gives a date, but the honest range around it is 4 to 13 months. If you know the dates of the last two heats, your own dog gap is a much better predictor, because individual dogs are far more consistent than the breed-wide range suggests.
- Do big dogs and small dogs cycle differently?
- Merck gives one range for the dog rather than separate figures by size, so we do not publish a size-specific prediction. Large breeds are often reported as cycling less frequently, but we have not found that stated with a figure in a source we would cite.
- My dog has not had a heat for over a year. Is that a problem?
- It is outside the normal 4 to 13 month range, so it is worth a conversation with your vet rather than something to work out from a calculator. There are several ordinary explanations and some that need looking at.
- Can I use this to time a mating?
- No. This tool predicts roughly when a heat will start. Timing a mating needs progesterone testing during the heat itself, done by a vet. Nothing on this page is precise enough for that.
- Can I use this as a form of birth control?
- No. A predicted date with a nine-month range around it is no basis for deciding when a dog can be off lead near intact males. If you do not want a litter, talk to your vet about the options.
Method
How we calculate this
Every figure on this page comes from one page of the Merck Veterinary Manual and was checked against it on the date shown. Where Merck gives an average and a range, we show both. The full method is on the how we calculate page.
Sources
1 source behind the figures on this page.
Breeding Management of Dogs and Cats
Merck Veterinary Manual - read 2026-10-08
merckvetmanual.com
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Last reviewed . Estimate only. For health questions, ask your vet.