Work backwards from a due date to the likely conception window.
How to use this calculator
Every field updates the result as you type — there is no submit step. The inputs below are pre-filled with a realistic example so you can see how the tool behaves before entering your own figures.
| Field | Unit | What it means |
|---|---|---|
| Due date | date | Pick a date from the calendar. |
| Cycle length | days | Enter a numeric value. |
Worked example
Using the default values loaded into the calculator above, the result is:
| Input | Value |
|---|---|
| Due date | 2027-02-08 |
| Cycle length (days) | 28 |
| Output | Value |
|---|---|
| Most likely conception date | Monday, May 18, 2026 |
| Conception window | Wednesday, May 13, 2026 → Tuesday, May 19, 2026 |
| Last menstrual period | Monday, May 4, 2026 |
| Implantation (approx.) | Wednesday, May 27, 2026 |
Reading the result
Health calculators apply population-level equations to an individual. They are screening and planning aids, useful for tracking direction over time, but they cannot account for your medical history, medication or body composition.
This is general information, not medical advice. Discuss anything that concerns you with a qualified clinician.
Sharing and saving a calculation
The "Copy link" button encodes every value you have entered into the page URL. Opening that link restores the calculation exactly, which makes it easy to bookmark a scenario, send it to someone else, or keep several variations side by side in separate tabs.
Frequently asked questions
What does the Pregnancy Conception Calculator do?
Work backwards from a due date to the likely conception window.
What result do the default values produce?
With the values pre-loaded in the calculator, most likely conception date comes to Monday, May 18, 2026.
Is this calculator free to use?
Yes. It is free, requires no account, and runs entirely in your browser — nothing you enter is transmitted or stored on a server.
Can I save or share a calculation?
Yes. The "Copy link" button builds a URL containing all your entered values. Anyone opening that link sees the same calculation.
How accurate is the result?
The calculation itself is exact for the inputs given. Real-world accuracy depends on how well those inputs reflect your actual situation, so review the assumptions before relying on the figure.