How Often Do Dogs Go Into Heat?

Owners of female dogs live with a calendar they cannot see. A heat arrives, and the question is when the next one will come. The answer, on average, is “about every seven months”, but the average hides a wide spread, and your own dog’s rhythm is what counts. This guide explains how often dogs normally go into heat, how size and age change the pattern, how to find your own dog’s interval, and how to plan around it. For what happens during a heat and how long it lasts, see our guide on how long a dog stays in heat.

The interval between heats

The time from the start of one heat to the start of the next is the interestrous interval. For dogs it averages about 7 months and the usual range is 4 to 12 months (Merck Veterinary Manual; Concannon 2011). That means most dogs have a heat roughly twice a year, some have it more often and a few only once a year. Most of the interval is the long resting stage between cycles, called anestrus, which explains why the gap varies so much between dogs.

What the calendar looks like

For a dog whose last heat started on 1 September 2026, the next heat is expected at:

The dates use average stage lengths of about 9 days each for proestrus and estrus, which vary in real dogs. The Dog Heat Cycle Calculator does the sum with your own last date and interval.

First heat and size

The first heat can come from around 6 months to about 2 years, depending on the dog. In general:

These are tendencies, not rules. If you are not sure about your dog’s age, the Dog Age Calculator shows her size class and life stage, and our dog age chart explains how size affects ageing. If she has not had a heat by 2 years, speak to your vet.

Why the interval varies

• Size and breed. Smaller dogs often cycle more often; some breeds have a typical pattern.
• Age. Young dogs are less regular, and older dogs can change.
• The individual dog. Dogs differ, even within the same litter.
• Health. Illness or other health factors can alter the cycle.

Because of this, the average is a starting point. After two or three heats, use your own dog’s record instead.

How to track it

Write down the first day of each heat, which is when you first see swelling or discharge, and how long it lasts.

After the second heat, you have a gap to work with. After the third, you can see how consistent she is. If the gaps are 6, 7 and 6.5 months, expect the next at about 6.5; if they are 5, 8 and 6, use the middle value and allow a margin of a few weeks.

A worked example

Bella’s heats started on 1 March 2026 and 1 September 2026.

1. Gap: 6 months.
2. Next heat expected: around 1 March 2027.
3. Because the first gap is from only one pair of dates, the owner treats it as approximate and starts watching about two weeks earlier, from mid-February.
4. When the third heat starts, the owner updates the record and recalculates.

The owner also notes that a young dog’s pattern can shift, so the estimate is revisited each time.

Why it matters

Knowing when the next heat is due helps you:

• Prevent an unplanned litter, by planning supervision and secure fences.
• Plan travel and boarding, since many kennels do not accept dogs in season.
• Plan neutering, with your vet’s advice on timing.
• Notice problems: a change in pattern, such as a very short or very long gap, is worth mentioning to your vet.

If you plan a litter, your vet can use progesterone tests to time mating more precisely; see our guide to how long dogs are pregnant for what follows.

When to call the vet

Speak to your vet if:

• There is no heat by 2 years of age.
• A heat lasts more than 4 weeks.
• The interval suddenly changes, with very frequent or very rare heats.
• She is unwell after a heat, for example with a discharge, drinking more or vomiting, which can be urgent.

Common mistakes

• Assuming the interval is exactly 6 months.
• Counting from the end of the heat instead of the start.
• Not recording the dates.
• Using a young dog’s first intervals as a firm pattern.
• Assuming a dog is safe from mating outside the heat dates you expect.
• Ignoring a change in pattern.

Why the interval matters for planning a litter

Breeders and owners who want puppies need to plan around the cycle. Because the interval varies, it helps to look at several heats before planning. Some practical points:

• Your vet may recommend waiting until a dog is fully mature before breeding, and the right age depends on breed and size. Ask your vet.
• Progesterone testing during estrus can pinpoint the best day for mating, and your vet can arrange it.
• The window of fertility is not the same for every dog, so do not rely on counting days alone.
• If you do not want a litter, the safest approach is to keep her away from intact males for the whole heat and discuss neutering with your vet.

Our guide to how long dogs are pregnant explains the timeline after mating.

Seasonal patterns

Some owners believe that dogs come into heat in particular seasons, but dogs are not strictly seasonal in the way some animals are, and the cycle depends on the individual. Some breeds have a tendency to cycle at a certain time of year, and a dog’s own history is the best guide. Keep a record of the months in which your dog’s heats start and look for a pattern over two or three years.

Dog heat versus cat heat

Cats cycle differently from dogs. A queen comes into heat repeatedly through the breeding season and ovulates in response to mating, while a bitch has one heat followed by a long rest, with ovulation during estrus. If you share a house with both, you will see different patterns. Our guide to how long cats are pregnant covers the cat side.

A worked record

Here is how a record might look after three heats.

The gaps are close to 7 months, so the owner expects the next heat around 16 to 20 December 2026, and starts watching from the beginning of December. If the next one comes at a very different time, that is useful information for the vet.

Why the interval varies

The heat interval used by the Dog Heat Cycle Calculator is about 7 months, with a range of 4 to 12. The range is wide because dogs differ by breed, size and age. Many small breeds cycle a little more often, and some large and giant breeds less often. The first heat can come at a different age depending on breed. Your own dog’s history is the best guide, so record the start date each time.

Predicting the next one

If the last heat began on 1 March and your dog’s interval is about 7 months, the next is expected around the start of October. With the range of 4 to 12 months, the window runs from early July to the following March. The wide window shows why a diary of your dog’s own gaps is more useful than any average. After two or three cycles you will see a pattern.

What the stages look like

A heat has stages, with proestrus and estrus each lasting about 9 days, though the length varies. See signs a dog is in heat for what to watch. The gap between heats starts counting from the beginning of one to the beginning of the next.

Quick summary

1. Dogs go into heat about every 7 months on average, with a range of 4 to 12 months.
2. Small breeds often cycle more often; large and giant breeds may have longer gaps and a later first heat.
3. From a start on 1 September, the next heat is around 1 April at 7 months, 1 March at 6 months, 1 January at 4 months.
4. Track the start date of each heat; after 2 or 3 cycles you can predict your own dog.
5. Call the vet for no heat by 2 years, a heat longer than 4 weeks or a sudden change.
6. Use the Dog Heat Cycle Calculator for the next date.

Frequently asked questions

Sources

1. Merck Veterinary Manual (pet owner version) — Management of Reproduction in Dogs
2. Concannon P.W. (2011) Reproductive cycles of the domestic bitch. Animal Reproduction Science 124:200-210
3. Cornell University College of Veterinary Medicine — Dog estrous cycles

Related calculators

• Dog Heat Cycle CalculatorPredict your dog's next season and the stages of the heat cycle.
• Dog Pregnancy Due Date CalculatorEstimate your dog's due date and the normal whelping window.
• Dog Age CalculatorConvert your dog's age into human years, taking size into account.

Keep reading

• How Long Does a Dog Stay in Heat? StagesA dog's heat usually lasts about 2 to 3 weeks and comes around every 7 months on average. Learn the four stages, how often it happens and when to call the vet.
• Signs a Dog Is in HeatSigns a dog is in heat: vulval swelling, bloody then paler discharge, behaviour changes, interest from males, how the signs change by stage and when to call the vet.
• Dog Pregnancy Week by WeekDog pregnancy week by week from the mating date: day ranges for each week, a worked calendar, tasks and vet questions for each stage, and when to call the vet.
• Dog Heat vs Phantom Pregnancy: What Is Going On?How to tell a dog in heat from a phantom pregnancy: the timeline after a heat, signs of false pregnancy, why only a vet can tell it from real pregnancy.