Dog Heat Cycle Calculator
Estimate when your dog's next heat may start, from the first day of the last one.
Next heat may start around
Thursday, October 1, 2026
- Estrus (receptive stage) begins about
- Saturday, October 10, 2026
- Estrus ends about
- Monday, October 19, 2026
- Earliest likely (4 months)
- Wednesday, July 1, 2026
- Latest likely (13 months)
- Thursday, April 1, 2027
Heat cycles come about every 7 months at your setting, but they vary, so treat the dates as a guide.
Calculation breakdown
| Step | Formula | Result |
|---|---|---|
| Days to the next heat | 2026-03-01 + 7 months | 214 days |
| Proestrus plus estrus | 9 days of proestrus + 9 days of estrus | 18 days |
How it works
Enter the first day of the last heat. The default interval is 7 months, the Merck average.
Worked example
A heat began on March 1, 2026, with a 7-month interval:
- Next heat: October 1, 2026
- Estrus begins about 9 days later: October 10, 2026
- Estrus ends about 9 days after that: October 19, 2026
Range
The earliest and latest dates use the 4- and 13-month limits from the same source.
Sources
Frequently asked questions
How often does a dog go into heat?
Female dogs usually have estrous cycles twice a year, but the interval can range from 4 to 13 months. The Merck Veterinary Manual gives an average of 7 months. Some large breeds, such as Great Danes, may cycle every 9 to 12 months.
How long does a dog heat last?
Proestrus, when bleeding and swelling start, lasts about 9 days on average, with a range of 2 days to 3 weeks. Estrus, when a female dog accepts a male, is also about 9 days on average, from as short as 3 days to as long as 3 weeks.
How does the calculator predict the next heat?
It adds your chosen interval in months to the first day of the last heat. Dogs are not exact, so use the earliest and latest dates as a range, and watch your dog for signs.
What is the first day of a heat?
Use the first day you notice vulvar swelling or a bloody discharge. This is the start of proestrus. Counting from the same sign each time gives the most consistent interval.
Can I use this to plan breeding?
Not on its own. The dates are an estimate. Breeding timing is best planned with your vet, who can test hormones to find ovulation.
Estimates for information only. Cycles vary between dogs, and a vet should advise on health or breeding.