Female dogs that have not been spayed come into heat, usually twice a year, and each cycle brings behaviour changes, bleeding and a fertile window. Owners often feel caught out by the first cycle, or unsure when the next one will arrive. This free calendar predicts future cycles from the dates of past cycles, using the average interval between them. It is an educational prediction only. Real cycles vary, especially in young dogs and older dogs, and only your vet can advise on breeding, spaying and any health concern.
To use the calendar, enter the start date of the most recent cycle, and add earlier cycle starts if you know them. With two or three dates, the tool calculates the average interval and predicts the next start. It also shows a typical fertile window around nine to fourteen days after the predicted start. Keep a record of every cycle, because a pattern built from your own dog’s dates beats any general average. If your dog has had only one cycle, the tool uses a typical interval of about 180 days, and the prediction is correspondingly rough.
Here is a worked example. A dog whose cycles started on 1 January and 31 January has an interval of 30 days in this simplified example, which would be unusually short, so the tool would predict 2 March next. Real intervals are usually much longer, often around six months, so a dog whose cycles started on 1 January and 1 July has an interval of 181 days and a next prediction around 30 December. The fertile window for that prediction falls roughly nine to fourteen days after the start. These are guides for planning, not guarantees, and a cycle can arrive weeks early or late without anything being wrong.
Knowing the cycle helps with practical planning. During heat, a female dog needs supervision outdoors, because males can appear from surprising distances and fences are not always enough. Keep walks on a lead, avoid off-lead parks during the fertile window, and never leave a female in heat unsupervised in a garden. At home, washable bedding and dog nappies help with bleeding. Some dogs become clingy, restless or less interested in food during heat, while others change barely at all. All of that variation is normal.
The most common mistake is assuming a cycle will arrive exactly on schedule and planning breeding or travel around that assumption. Another mistake is believing a first cycle means a dog is ready to breed. Physical maturity and the right age for breeding are vet questions, and breeding carries real risks for the mother and the puppies. A third mistake is missing the signs of a problem: a cycle that lasts far longer than usual, a foul smelling discharge, fever, lethargy or excessive thirst after a cycle all deserve prompt vet attention, because they can signal infection.
Spaying is a decision to discuss with your vet, not a default. It prevents unwanted litters and removes the risk of some serious conditions, but the best timing depends on breed, size and health, and it is a surgical decision with its own risks. If you do not plan to breed, ask the vet about timing at a routine visit, well before the next cycle. If you do plan to breed, ask about health tests, the right age and the care a pregnant dog needs. The calendar supports either choice by making the timing visible.
Keep cycle records for the life of the dog. Note the start date, the length of bleeding, behaviour changes and any unusual signs. A long record helps the vet spot irregular patterns early, and it helps you plan around future cycles without surprises. If cycles stop, become very irregular or change sharply in an older dog, mention it at the next visit rather than waiting for the annual checkup. A simple calendar, kept honestly, turns a confusing part of dog ownership into a predictable routine.
Spanish version: Calendario de celo en perras – Seguimiento y predicción orientativa