Your dates
Estimate the next heat
Use the first day you noticed bloody discharge or clear heat signs.
Cycle planning tool
Dog Heat Cycle Calendar
Estimate a planning window from recorded heat-start dates, prepare for a puppy's first heat, or map the visible-sign period after a heat begins.
Quick answer: most dogs come into heat about twice per year, but a normal interval can vary from roughly 5 to 11 months. Calendar dates help with preparation, not fertility testing.
Planning, not diagnosis
Personal history is used before averages
The calendar never labels a date as a safe or exact fertile day. Veterinary testing is required for breeding timing.
Planning estimate only. This calendar cannot confirm cycle stage, ovulation, fertility, pregnancy, or the right time to breed.
5-11 months
Common interval rangeIndividual dogs may fall outside it.
6-24 months
Broad first-heat ageSmaller breeds often begin earlier.
14-21 days
Common visible-sign periodNot an exact fertile window.
Frequency
How often do dogs go into heat?
Most female dogs come into heat about twice per year, but there is no universal six-month schedule. Cornell describes an average interval of roughly 5 to 11 months, while Merck reports a wider overall range of 4 to 13 months and an average near 7 months.
Young dogs can be irregular for their first cycles. Small dogs may cycle as often as three times yearly, while giant breeds and some breeds such as Basenjis may cycle only once a year. Your own dog's recorded Day 1 dates are more useful than a size-only assumption.
Small dogsMay cycle more frequently than average.
Large and giant dogsMay have longer intervals between heats.
Young dogsCan take up to two years to develop a regular pattern.
Individual historyUse repeat dates before population averages.
First cycle
When do puppies go into heat?
A puppy's first heat can begin from about 6 to 24 months of age. Smaller breeds tend to reach puberty earlier. Large and giant breeds may not have a first heat until 18 months to 2 years.
The calculator deliberately shows a broad planning range. A puppy's weight, breed size, or birthday cannot produce one reliable first-heat date.
Before 6 months
Most puppies are still before the broad expected range, although individual exceptions occur.
6-12 months
Many small and medium dogs experience their first heat during this period.
12-18 months
Later first heats remain common in larger dogs.
18-24 months
Large and giant breeds may first cycle near the later end of the range.
Stages of the canine heat cycle
How long does a dog heat cycle last?
The visible period commonly called heat often lasts about 14 to 21 days. The complete reproductive cycle is much longer and includes four stages. Stage timing varies enough that a calendar cannot diagnose which stage a dog is in.
| Stage | Typical timing | What owners may notice |
|---|---|---|
| Proestrus | Average 6-11 days | Vulvar swelling and bloody discharge; males may be attracted, but the female is usually not receptive. |
| Estrus | Often 5-9 days; reported range 1-20 | Discharge may lighten and the female may become receptive. Calendar timing cannot confirm ovulation. |
| Diestrus | About 2 months | Visible heat signs end, while progesterone remains elevated whether or not pregnancy occurred. |
| Anestrus | Often several months | A resting and uterine-recovery period before the next cycle begins. |
Recognizing heat
How to know when your dog is in heat
The first sign owners notice is often bloody discharge, but signs can be subtle and the amount varies between dogs.
Physical signs
- Swelling or enlargement of the vulva
- Bloody discharge that may become lighter
- More frequent urination or marking
- Increased licking of the genital area
Behavior and dog interactions
- Restlessness, clinginess, withdrawal, or appetite changes
- Greater attention from male dogs
- Tail position changes or flagging
- Escape attempts or increased interest in other dogs
Visible signs do not reliably identify fertility. Keep an intact female separated from intact males for the full observed heat and follow your veterinarian's advice.
After spaying
Can a spayed dog go into heat?
A fully spayed dog should not have heat cycles. Heat-like signs after surgery can occur if functional ovarian tissue remains, a condition called ovarian remnant syndrome.
Vulvar swelling, urine marking, flagging, behavioral changes, or attraction from male dogs after spaying should be assessed by a veterinarian rather than entered into a prediction calendar.
Urgent warning signs
Do not assume every discharge is heat
Pyometra is a potentially life-threatening uterine infection that often develops one to two months after a heat. Seek prompt veterinary care for:
- Foul-smelling, cream-colored, or pus-like discharge
- Lethargy, poor appetite, vomiting, fever, or weakness
- Increased thirst or urination
- A painful or enlarged abdomen, pale gums, or collapse
Transparent method
How the dog heat cycle calendar works
The calendar prioritizes your dog's own recorded Day 1 dates. With at least two observed intervals, it calculates the median gap and displays the historical minimum-to-maximum range. With one interval, it repeats that interval as a limited-history estimate.
If there is no personal interval, the result uses a broad 5-to-11-month population range and a 7-month planning midpoint. The "start watching" reminder begins 21 days before the earliest estimate as a preparation prompt, not a medical boundary.
interval = next recorded Day 1 - previous recorded Day 1
planning midpoint = last Day 1 + median observed interval
observed range = last Day 1 + shortest to longest recorded interval
What it cannot determine
- Ovulation or an exact fertile window
- Whether mating or pregnancy occurred
- The current hormone level or cycle stage
- The cause of a missed, prolonged, or unusual cycle
- Whether a dog is medically ready to breed
Questions
Dog Heat Cycle Calendar FAQ
Most dogs have about two heats per year, but intervals vary widely. Cornell reports an average interval of about 5 to 11 months. Small dogs may cycle more often, while some giant or primitive breeds cycle about once yearly.
A first heat may begin from about 6 to 24 months of age. Smaller breeds tend to begin earlier, while large and giant breeds may not have a first heat until 18 months to 2 years.
The visible part commonly called heat usually includes proestrus and estrus. Bloody discharge often lasts about 14 to 21 days, but each stage and each dog's signs can be shorter or longer.
Twice yearly is common, but it is not a fixed schedule. Small dogs may cycle three times per year, while giant breeds and breeds such as Basenjis may cycle only once yearly.
Common signs include vulvar swelling, bloody discharge, increased licking or urination, behavior changes, and increased attention from male dogs. Signs vary, and some heats are difficult to notice.
A fully spayed dog should not have heat cycles. Heat-like signs after spaying require veterinary assessment because remaining functional ovarian tissue, called ovarian remnant syndrome, is one possible cause.
No. Stage lengths and ovulation timing vary too much for calendar dates or visible signs to identify fertility reliably. Planned breeding requires veterinary timing such as progesterone testing or vaginal cytology.
Seek prompt veterinary care for foul-smelling or pus-like discharge, lethargy, vomiting, poor appetite, increased thirst or urination, a painful or enlarged abdomen, weakness, collapse, or heat signs after spaying.
Research Methodology and references Cycle ranges, stage descriptions, spayed-dog context, and emergency signs are tied to veterinary references.
The calendar combines Cornell's owner-facing cycle ranges, Merck's reproductive-management intervals and stage descriptions, VCA's puberty and frequency context, and veterinary references for ovarian remnant syndrome and pyometra. Population ranges are never presented as exact dates for an individual dog.
- Cycle overviewCornell University College of Veterinary Medicine: Dog estrous cycles Open
- Intervals and stagesMerck Veterinary Manual: Management of Reproduction in Dogs Open
- First heat and frequencyVCA Animal Hospitals: Estrous Cycles in Dogs Open
- After spayingMerck Veterinary Manual: Ovarian Remnant Syndrome Open
- Emergency contextCornell University College of Veterinary Medicine: Pyometra Open
Planning estimates only. Not veterinary advice. Last reviewed July 26, 2026.