{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"ovulation"},"result":{"entity_type":"calculator","id":"ovulation","calculator_id":"ovulation","canonical_url":"https://tttkmbb.com/health/ovulation","name":"Ovulation Calculator","title":"Ovulation and Fertile Window Calculator from Last Period and Cycle Length","category":"health","category_name":"Health","tool_name":"calculate_ovulation_date","featured_mcp_tool":false,"description":"Estimates the ovulation date, the six-day fertile window and the next period start from the first day of the last period and the average cycle length.","use_when":"You want to estimate the most fertile days of a regular menstrual cycle.","do_not_use_when":"Cycles vary by more than a few days, hormonal contraception is used, or you need contraception (calendar estimates are not reliable for preventing pregnancy).","inputs":[{"name":"last_period_date","label":"First day of last period","type":"date","required":true,"description":"First day of the most recent period (YYYY-MM-DD).","example":"2026-09-01"},{"name":"cycle_length_days","label":"Cycle length","type":"integer","unit":"days","required":false,"default":28,"min":20,"max":45,"description":"Average number of days from one period start to the next.","example":28},{"name":"luteal_phase_days","label":"Luteal phase","type":"integer","unit":"days","required":false,"default":14,"min":10,"max":18,"description":"Days from ovulation to the next period; 14 is the population average.","example":14}],"outputs":[{"name":"ovulation_date","label":"Estimated ovulation","type":"date","decimals":4,"description":"Next period start minus the luteal phase."},{"name":"fertile_window_start","label":"Fertile window starts","type":"date","decimals":4,"description":"Five days before ovulation (sperm survival)."},{"name":"fertile_window_end","label":"Fertile window ends","type":"date","decimals":4,"description":"Ovulation day."},{"name":"next_period_date","label":"Next period expected","type":"date","decimals":4,"description":"LMP + cycle length."},{"name":"pregnancy_test_date","label":"Earliest reliable pregnancy test","type":"date","decimals":4,"description":"Day of the expected next period."}],"input_schema":{"type":"object","properties":{"last_period_date":{"description":"First day of the most recent period (YYYY-MM-DD).","type":"string","format":"date","examples":["2026-09-01"]},"cycle_length_days":{"description":"Average number of days from one period start to the next. Unit: days.","type":"integer","minimum":20,"maximum":45,"default":28,"examples":[28],"x-unit":"days"},"luteal_phase_days":{"description":"Days from ovulation to the next period; 14 is the population average. Unit: days.","type":"integer","minimum":10,"maximum":18,"default":14,"examples":[14],"x-unit":"days"}},"additionalProperties":false,"required":["last_period_date"]},"output_schema":{"type":"object","properties":{"ovulation_date":{"description":"Next period start minus the luteal phase.","type":"string","format":"date"},"fertile_window_start":{"description":"Five days before ovulation (sperm survival).","type":"string","format":"date"},"fertile_window_end":{"description":"Ovulation day.","type":"string","format":"date"},"next_period_date":{"description":"LMP + cycle length.","type":"string","format":"date"},"pregnancy_test_date":{"description":"Day of the expected next period.","type":"string","format":"date"}}},"formula":"next_period = LMP + cycle_length; ovulation = next_period − luteal_phase; fertile_window = ovulation − 5 … ovulation","sources":[{"name":"Wilcox AJ, Weinberg CR, Baird DD (1995) Timing of sexual intercourse in relation to ovulation, N Engl J Med 333:1517-1521","url":"https://pubmed.ncbi.nlm.nih.gov/7477165/","type":"peer_reviewed","retrieved_at":"2026-09-23"},{"name":"NHS – Trying to get pregnant: when am I most fertile?","url":"https://www.nhs.uk/pregnancy/trying-for-a-baby/trying-to-get-pregnant/","type":"reference","retrieved_at":"2026-09-23"}],"freshness":{"type":"static","max_age_seconds":null,"note":"Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output."},"examples":[{"name":"LMP 2026-09-01, 28-day cycle","inputs":{"last_period_date":"2026-09-01","cycle_length_days":28},"expected":{"ovulation_date":"2026-09-15","fertile_window_start":"2026-09-10","fertile_window_end":"2026-09-15","next_period_date":"2026-09-29"},"url":"https://tttkmbb.com/api/v1/calculate/ovulation?last_period_date=2026-09-01&cycle_length_days=28"}],"faq":[{"q":"How reliable is the estimate?","a":"Ovulation timing varies even in regular cycles; ovulation predictor kits or basal body temperature tracking are more precise than calendar methods."}],"tags":["ovulation","fertile window","fertility","cycle","next period"],"related":[{"calculator_id":"pregnancy-due-date","reason":"Once pregnant, estimate the due date from the same LMP."}],"links":{"html":"https://tttkmbb.com/health/ovulation","markdown":"https://tttkmbb.com/health/ovulation.md","json":"https://tttkmbb.com/health/ovulation.json","api":"https://tttkmbb.com/api/v1/calculate/ovulation","schema":"https://tttkmbb.com/api/v1/calculators/ovulation","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-23"},"timestamp":"2026-09-23T23:28:35Z","next_actions":[{"tool":"run_calculator","calculator_id":"ovulation","reason":"Run Ovulation Calculator with the inputs above."}],"links":{"markdown":"https://tttkmbb.com/health/ovulation.md"}}