Due Date Calculator
Estimate a due date from LMP or a known conception date, then view gestational age and time remaining for your chosen as-of date.
Calculator arithmetic runs locally in your browser and does not require an API.
The interactive calculator loads here when JavaScript is enabled.
How to use Due Date Calculator
Choose the date method before entering a date. Known conception is an input assumption, not something this tool establishes. The as-of date must follow the entered date within the supported range.
Formula and method
LMP mode adds 280 days. Known-conception mode adds 266 days and infers an LMP 14 days earlier for gestational age. Both methods use calendar days rather than a fixed number of months.
Understanding the results
The date is a reference estimate, not a promised delivery day. Ultrasound and clinical dating may revise an LMP-based estimate. IVF transfer dates and cycle-length adjustments are not supported, and the tool cannot determine pregnancy status.
Worked example
Using a known conception date of February 29, 2024 with an as-of date of March 1, 2024 gives an estimated due date of November 21, 2024, after adding 266 calendar days.
Pregnancy and conception dates are estimates. A healthcare professional can provide guidance based on your individual situation.
References
Frequently asked questions
Will delivery occur on this date?
The calculator cannot predict an exact delivery day; actual timing varies.
Can this use an IVF transfer date?
No. The supported inputs are LMP or a known conception date, not embryo transfer details.
Why is gestational age longer than time since conception?
The conception model starts the gestational clock at an inferred LMP 14 days earlier.