Pregnancy by Conception Date
Know your conception date? Calculate your due date, gestational age, trimester, and key pregnancy milestones — no LMP date needed.
- Due date = Conception + 266 days
- LMP = Conception − 14 days (standard ovulation offset)
- Gestational age is counted from LMP, not conception
| Week | Date | Milestone | Status |
|---|---|---|---|
| Enter your conception date to see milestones | |||
Already know your conception date? Calculate your estimated due date, current gestational age, trimester, and pregnancy milestones without needing your last menstrual period.
How Pregnancy by Conception Date Calculator Works
Unlike LMP-based due date calculators, this tool works forward from a known or estimated conception date: due date = conception date + 266 days (38 weeks) — 266 rather than 280 because conception itself already accounts for the roughly two weeks between LMP and ovulation.
To keep gestational age consistent with standard obstetric convention (which is always counted from LMP, not conception), the calculator first works backward to an equivalent LMP: LMP = conception date − 14 days, using the typical ovulation offset. All gestational age, trimester, and milestone calculations then run from that estimated LMP exactly as they would with a directly entered one.
This method is especially useful for pregnancies conceived via a known ovulation date, fertility tracking, or a single-encounter timeframe, where the conception date is known more precisely than a memory of the last period.
See It In Action
Who Uses Pregnancy by Conception Date Calculator and Why
- Estimating a due date when you know your conception date precisely — for example, from ovulation tracking or a single-encounter timeframe.
- Cross-checking a due date that was originally calculated from LMP, using a known or estimated conception date instead.
- Getting a consistent gestational age figure that matches what a doctor would use, even though you started from a conception date rather than LMP.
Mistakes to Avoid
- Entering an estimated conception date with more confidence than it deserves — even careful tracking can be off by a few days, since ovulation timing varies cycle to cycle.
- Expecting a different due date than an LMP-based calculator would give for the same pregnancy — when the dates are consistent, both methods converge on the same result, so a big mismatch usually points to one of the input dates being off.
Tips for Best Results
- This tool is most useful when you have a well-tracked ovulation date (from ovulation predictor kits or basal body temperature) rather than a rough guess.
- If your conception date estimate and your LMP-based estimate disagree by more than a few days, an early ultrasound is the most reliable way to resolve the discrepancy.
Fixing Common Problems
My due date here is different from an LMP-based calculator I used elsewhere. — Check whether your LMP date and conception date are actually 14 days apart as the standard assumption expects — if your cycle is longer or shorter than 28 days, the two methods can diverge unless you account for that.
Terms Explained
Equivalent LMP: The last-menstrual-period date the calculator derives by subtracting 14 days from your entered conception date, used to keep gestational age consistent with standard prenatal convention.