{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"pregnancy-due-date"},"result":{"entity_type":"calculator","id":"pregnancy-due-date","calculator_id":"pregnancy-due-date","canonical_url":"https://tttkmbb.com/health/pregnancy-due-date","name":"Pregnancy Due Date Calculator","title":"Pregnancy Due Date Calculator – Naegele's Rule from Last Menstrual Period","category":"health","category_name":"Health","tool_name":"calculate_pregnancy_due_date","featured_mcp_tool":false,"description":"Estimates the due date, conception date and current gestational age from the first day of the last menstrual period, adjusting for cycle length (Naegele's rule).","use_when":"You know the first day of the last period and want the estimated due date, trimester dates or gestational age on a given date.","do_not_use_when":"Cycles are very irregular, the LMP is unknown, or an ultrasound dating is available (ultrasound dating in the first trimester is more accurate and takes precedence).","inputs":[{"name":"last_period_date","label":"First day of last period","type":"date","required":true,"description":"First day of the last menstrual period (ISO date YYYY-MM-DD).","example":"2026-01-01"},{"name":"cycle_length_days","label":"Cycle length","type":"integer","unit":"days","required":false,"default":28,"min":20,"max":45,"description":"Average menstrual cycle length; the due date shifts by (cycle − 28) days.","example":28},{"name":"as_of_date","label":"Gestational age as of","type":"date","required":false,"description":"Optional date on which to report gestational age (weeks + days). Omit to skip.","example":"2026-04-15"}],"outputs":[{"name":"due_date","label":"Estimated due date","type":"date","decimals":4,"description":"LMP + 280 days + (cycle − 28)."},{"name":"conception_date_estimate","label":"Estimated conception","type":"date","decimals":4,"description":"Approximately LMP + 14 days + (cycle − 28)."},{"name":"second_trimester_start","label":"Second trimester starts","type":"date","decimals":4,"description":"Week 14 (day 91 of pregnancy)."},{"name":"third_trimester_start","label":"Third trimester starts","type":"date","decimals":4,"description":"Week 28 (day 189)."},{"name":"gestational_age","label":"Gestational age","type":"string","decimals":4,"description":"Weeks and days as of as_of_date (only when as_of_date is given)."},{"name":"gestational_days","label":"Gestational days","type":"integer","unit":"days","decimals":4,"description":"Days since LMP as of as_of_date (only when given)."}],"input_schema":{"type":"object","properties":{"last_period_date":{"description":"First day of the last menstrual period (ISO date YYYY-MM-DD).","type":"string","format":"date","examples":["2026-01-01"]},"cycle_length_days":{"description":"Average menstrual cycle length; the due date shifts by (cycle − 28) days. Unit: days.","type":"integer","minimum":20,"maximum":45,"default":28,"examples":[28],"x-unit":"days"},"as_of_date":{"description":"Optional date on which to report gestational age (weeks + days). Omit to skip.","type":"string","format":"date","examples":["2026-04-15"]}},"additionalProperties":false,"required":["last_period_date"]},"output_schema":{"type":"object","properties":{"due_date":{"description":"LMP + 280 days + (cycle − 28).","type":"string","format":"date"},"conception_date_estimate":{"description":"Approximately LMP + 14 days + (cycle − 28).","type":"string","format":"date"},"second_trimester_start":{"description":"Week 14 (day 91 of pregnancy).","type":"string","format":"date"},"third_trimester_start":{"description":"Week 28 (day 189).","type":"string","format":"date"},"gestational_age":{"description":"Weeks and days as of as_of_date (only when as_of_date is given).","type":"string"},"gestational_days":{"description":"Days since LMP as of as_of_date (only when given). Unit: days.","type":"integer","x-unit":"days"}}},"formula":"due_date = LMP + 280 days + (cycle_length − 28); conception ≈ LMP + 14 + (cycle_length − 28); gestational_age = as_of_date − LMP","sources":[{"name":"ACOG Committee Opinion 700 (2017) Methods for Estimating the Due Date","url":"https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2017/05/methods-for-estimating-the-due-date","type":"standard","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 2026-01-01, 28-day cycle, as of 2026-04-15","inputs":{"last_period_date":"2026-01-01","cycle_length_days":28,"as_of_date":"2026-04-15"},"expected":{"due_date":"2026-10-08","conception_date_estimate":"2026-01-15","second_trimester_start":"2026-04-02","third_trimester_start":"2026-07-09","gestational_age":"14 weeks 6 days","gestational_days":104},"url":"https://tttkmbb.com/api/v1/calculate/pregnancy-due-date?last_period_date=2026-01-01&cycle_length_days=28&as_of_date=2026-04-15"},{"name":"LMP 2026-03-10, 32-day cycle","inputs":{"last_period_date":"2026-03-10","cycle_length_days":32},"expected":{"due_date":"2026-12-19"},"url":"https://tttkmbb.com/api/v1/calculate/pregnancy-due-date?last_period_date=2026-03-10&cycle_length_days=32"}],"faq":[{"q":"How accurate is the due date?","a":"Only about 4% of babies arrive on the estimated date; most are born within two weeks either side. First-trimester ultrasound refines the estimate."},{"q":"How are trimesters defined?","a":"Following ACOG: first trimester through 13 weeks 6 days, second from 14 weeks 0 days, third from 28 weeks 0 days."}],"tags":["due date","pregnancy","naegele","gestational age","conception date","trimester"],"related":[{"calculator_id":"ovulation","reason":"Estimate fertile window and ovulation for a cycle."},{"calculator_id":"date-difference","reason":"General date arithmetic."}],"links":{"html":"https://tttkmbb.com/health/pregnancy-due-date","markdown":"https://tttkmbb.com/health/pregnancy-due-date.md","json":"https://tttkmbb.com/health/pregnancy-due-date.json","api":"https://tttkmbb.com/api/v1/calculate/pregnancy-due-date","schema":"https://tttkmbb.com/api/v1/calculators/pregnancy-due-date","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-23"},"timestamp":"2026-09-23T23:32:17Z","next_actions":[{"tool":"run_calculator","calculator_id":"pregnancy-due-date","reason":"Run Pregnancy Due Date Calculator with the inputs above."}],"links":{"markdown":"https://tttkmbb.com/health/pregnancy-due-date.md"}}