Dog heat cycle calculator
Most dogs come into heat about every six months, and each heat lasts two to three weeks. She's usually most fertile around days 9 to 14, but only progesterone tests from a vet can pin down ovulation.
Free, no sign-up · Reviewed October 2026 · How it works
The day you first noticed swelling or spotting.
After two or three cycles, her own pattern is a better guide than any average.
Estimates, not a contraceptive
Cycles vary from dog to dog and from one heat to the next, and a dog can become pregnant on any day of estrus. Don't rely on these dates to prevent or plan a pregnancy; your vet can time ovulation with progesterone tests. Ask your vet if her heats are less than 4 months apart, last longer than 3 weeks, or come with lethargy, heavy drinking or pus-like discharge.
How this tool works
The calculator counts from the first day of her last heat (the day you first saw swelling or spotting) and shows the typical phases: proestrus around days 1 to 9, the likely fertile window around days 9 to 14, and the end of estrus around day 21.
It predicts her next three heats using the typical gap for her size (small dogs more often, giant dogs less often) or the gap you enter. Her own pattern, once you've logged a few heats, is the best guide.
Don't use these dates to prevent or plan a pregnancy: she can conceive on any day of estrus.
Questions.
How often do dogs go into heat?
Usually about every six months. Small breeds can cycle every four to five months and giant breeds every 12 to 18 months.
How long does a dog stay in heat?
Two to three weeks from the first signs, though it varies.
When does a puppy have her first heat?
Usually between 6 and 15 months, later in giant breeds.
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