by MarkMare Gestation CalculatorEstimate your mare’s foaling date and track pregnancy stages. Breeding Date ? Select the date of successful breeding (e.g., 2025-04-01). Gestation Period (days) ? Average is 340 days; range is 320–360 days (e.g., Thoroughbred: ~340, Draft: ~350). Calculate ResetEnter the breeding date, then click “Calculate”. JavaScript is disabled. Please enable it to use the calculator.