How to use this calculator
Choose the dating information you have. Pregnancy timing highlights an estimated conception date and distinguishes it from obstetric gestational age. The possible fertile intercourse interval uses the five days before estimated ovulation through the following day; it is not an exact conception window. Use your clinician’s established dating when available and avoid switching it solely because calendar methods differ.
- Enter dating information, calculate pregnancy age on, first day of last menstrual period and review the remaining options.
- Select Calculate or change a value to update the result. Read the result label and units before copying.
- Use Reset to restore the worked starting values.
Formula and method
A natural conception date cannot be identified exactly by this tool and must not be used to establish paternity. Obstetric age starts about two weeks before fertilization in a typical cycle. Early ultrasound and medically established dating may be more reliable. Irregular cycles weaken LMP estimates. Due dates are estimates, not guarantees of delivery on one day.
Worked example
For an LMP of 1 September 2026 and a 28-day cycle, the due date is 8 June 2027. The calendar conception estimate is 15 September 2026. On 12 November 2026 the gestational age is 10 weeks and 2 days.
Questions about pregnancy calculator
When did I get pregnant?
A calendar can estimate conception around two weeks after the gestational dating start, but it cannot determine exactly when natural fertilization occurred. Cycle timing varies. Use the dating method your clinician established; early ultrasound can be more reliable than a period-based estimate.
What assumptions should I check?
A natural conception date cannot be identified exactly by this tool and must not be used to establish paternity. Obstetric age starts about two weeks before fertilization in a typical cycle. Early ultrasound and medically established dating may be more reliable. Irregular cycles weaken LMP estimates. Due dates are estimates, not guarantees of delivery on one day.
Are my inputs saved?
Calculations run in your browser. We store only tool IDs for favorites and recent tools. Sharing inputs in links is disabled for this category.
Health tools provide general estimates, not diagnoses or personal medical advice. BMI offers a labeled CDC child/teen reference; adult screening bands must not be applied to children. Discuss health and exercise decisions with a qualified professional. Read the tool-specific sources below for background on the method.