Unspayed female dogs go into heat roughly every 6 months, though the interval can range from about 4 to 12 months depending on breed and the individual dog. This calculator projects your dog's next heat start date from her last one, and breaks down the four phases of the cycle so you know what to expect and when.

How the Dog Heat Cycle Calculator works

The calculator adds your chosen cycle interval — 6 months by default — to the date you enter for the start of your dog's last heat. That sum is the predicted next heat start date. Because real cycles vary, treat the result as a planning estimate rather than an exact date, especially for young dogs whose first few cycles are often irregular.

The Cycle Phases tab breaks a single heat down into four stages — proestrus, estrus, diestrus, and anestrus — anchored to whichever last-heat date you entered, so you can see roughly which phase your dog would be in on any given day of that cycle.

Inputs and what they mean

Last Heat Start Date is the day you first noticed signs of heat — typically vulvar swelling and light bleeding — not the day bleeding stopped. Cycle Interval defaults to 6 months, the commonly cited average, but ranges from about 4 months (some smaller breeds and individual dogs cycle more often) to 12 months (some larger breeds cycle less often). If you've tracked two or more of your dog's previous heats, use the interval you've actually observed instead of the default.

Limits and edge cases

This calculator uses a simple average-interval formula — it does not account for hormonal testing, progesterone timing, or breed-specific data, and it cannot detect pregnancy, false pregnancy, or a skipped cycle. A first heat typically arrives between 6 and 12 months of age, so the calculator isn't meaningful before a dog has had at least one recorded heat. If your dog's cycles are very irregular, unusually long, or she shows signs of illness during heat, talk to your veterinarian rather than relying on this estimate alone — and remember spaying permanently ends heat cycles if that's part of your plan.