Predict when your female dog will come into heat again. Enter the date her last heat started and her usual cycle length to see the next heat dates, the estimated fertile window and a colour-coded calendar, so you can plan walks, boarding and vet visits.
Last updated:
First day you noticed bleeding or a swollen vulva.
Time from one heat start to the next. Average is about 6 months.
days
Usually 2–4 weeks; 21 days is typical.
Enter your values to see the result.
Advertisement
Advertisement
How to use the Dog Heat Cycle Calculator
Pick the date the last heat started, the first day of bleeding or swelling.
Enter the cycle length in months or days; use your dog's own history if you know it.
Adjust how long a heat lasts if your dog's heats are shorter or longer than 21 days.
Press Calculate heat dates to see the next heat, the fertile window and a calendar.
Download the CSV or copy the dates to add them to your own calendar.
How the heat dates are predicted
Each future heat is the last start date plus a whole number of cycle lengths: next start = last start + k × cycle length. The heat end is start + duration − 1, and the fertile window is estimated at days 10–14 of a 21-day heat (scaled if you enter a different duration).
Example: last heat began March 1, cycle 6 months, heat 21 days → next heat about September 1 to September 21, most fertile around September 10–14.
Stages of the canine heat cycle
Stage
Typical length
What you see
Proestrus
about 9 days (3–17)
Swollen vulva, bloody discharge, males attracted but she refuses them
Estrus
about 9 days (3–21)
Discharge becomes lighter or straw-coloured; she accepts males; ovulation occurs
Diestrus
about 60 days
Heat signs fade; pregnancy or a hormonal phase that looks similar
Anestrus
about 4 months (varies)
Resting phase until the next proestrus
Typical heat intervals by size
Dog type
Interval between heats
Heats per year
Small breeds
4–6 months
2–3
Medium and large breeds
6–7 months
about 2
Giant breeds
8–12+ months
1–1.5
Basenji and some wolf-like breeds
about 12 months
1
Track a few cycles and use your dog's own average interval for the most accurate prediction. These dates are estimates and not a substitute for veterinary advice.
Frequently asked questions
How often do dogs go into heat?
Most female dogs come into heat about every 6 months, or twice a year. Small breeds can cycle every 4 to 5 months, and giant breeds may only cycle every 12 to 18 months. Some breeds, such as the Basenji, cycle once a year.
How long does a dog stay in heat?
A heat usually lasts 2 to 4 weeks, about 21 days on average. It starts with proestrus (swelling and bloody discharge, around 9 days), followed by estrus, when the female accepts a male (around 9 days, varying from 3 to 21).
When is a dog most fertile during heat?
Typically around days 10 to 14 after the first sign of bleeding, but ovulation timing varies a lot between dogs and even between heats. Vets use progesterone blood tests for exact timing. The calculator shows an estimate only.
At what age does a dog have her first heat?
Usually between 6 and 15 months: small breeds as early as 6 months, large and giant breeds often 12 to 24 months. The first few cycles can be irregular.
Can I rely on these dates to prevent pregnancy?
No. Dogs can come into heat earlier or later than predicted, and some heats are silent. Keep an intact female away from intact males from the first sign of heat until it is completely over, and talk to your vet about spaying.
Do dogs stop having heat cycles when they get older?
Dogs do not go through menopause. Intervals often get longer and heats less obvious with age, but an unspayed senior female can still cycle and still get pregnant.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.