How this calculator works
Merck describes an average interval of about seven months, with substantial breed and individual variation. Your dog's own records are more informative. Each reminder is calculated directly from the original start date, so clamping a month-end date does not shift later cycles. The tool uses calendar months rather than treating every month as 30 days.
Formula
Projected start number n = original heat start + n × interval in calendar months. If the target month lacks the original day, use its final day.
Worked example
Starting on 31 August 2026 with a six-month interval gives reminders for 28 February 2027, 31 August 2027 and 29 February 2028.
Advertisement
Frequently asked questions
When is my dog fertile?
This calendar cannot answer that. Reproductive examination and hormone testing may be needed for breeding management.
Is a longer interval always abnormal?
No. Some large breeds naturally have long intervals. Discuss a change from your dog's usual pattern with your veterinarian.
Can I use these dates as contraception?
No. Keep intact dogs appropriately separated and discuss reliable pregnancy prevention with your veterinarian.