Conception Calculator
Estimate your conception date, due date, and exactly how far along you are today — with a full trimester breakdown.
Results from this calculator are estimates provided for general informational purposes only, based on formulas, rates, and standards commonly accepted as of 2026. Figures may differ slightly from other calculators or professional sources due to rounding methods, differing assumptions, or regional regulations, and rules may change over time. Always consult a qualified professional — such as a financial advisor, healthcare provider, or other relevant specialist — before making decisions based on these results.
Estimated Due Date
Apr 15, 2027
Likely Conception Date
Jul 23, 2026
Conception window: Jul 18, 2026 – Jul 24, 2026
Example
With a last period starting July 9, 2026 and a 28-day cycle, conception most likely occurred around July 23, 2026, putting the estimated due date at April 15, 2027. As of today, that's 6 weeks and 0 days along — about 15.0% of the way through pregnancy, in the first trimester.
Pregnancy progress as of today
6 weeks, 0 days along
238 days until due date
1 of 3 trimesters
What is a Conception Calculator?
A conception calculator estimates when you conceived and projects your due date and current progress through pregnancy from a single starting point: the first day of your last period. It's built around Naegele's rule, the standard clinical method of adding 280 days (40 weeks) to the start of the last period to estimate a due date — the same convention used by most obstetricians and midwives.
Unlike a calculator that works backward from a known due date or ultrasound, this tool works forward from your last period to show your full pregnancy timeline at once: conception window, due date, current week, and trimester boundaries.
Trimester Breakdown
| Trimester | Weeks | Start | End |
|---|---|---|---|
| First Trimester (current) | Weeks 1-13 | Jul 9, 2026 | Oct 7, 2026 |
| Second Trimester | Weeks 14-27 | Oct 8, 2026 | Jan 13, 2027 |
| Third Trimester | Weeks 28-40 | Jan 14, 2027 | Apr 15, 2027 |
How This Calculator Works
Pregnancy is dated from the first day of the last menstrual period (LMP), not from the actual conception date — even though conception itself happens roughly two weeks later. This is purely a convention: LMP is a known, remembered date, while the exact conception date rarely is.
Conception itself is estimated using your cycle length: ovulation typically occurs 14 days before the next period, so a longer cycle pushes ovulation (and conception) later relative to the last period, and a shorter cycle pulls it earlier.
Why Due Dates Are Estimates, Not Guarantees
Only about 5% of babies are born on their exact due date. Naegele's rule assumes a textbook 28-day cycle with ovulation on day 14 — real cycles vary, and a first-trimester ultrasound (which measures the embryo directly) is generally considered more accurate than an LMP-based estimate, especially for irregular cycles.
What Happens in Each Trimester
The first trimester (weeks 1-13) covers the embryo's core organ development and carries the highest miscarriage risk. The second trimester (weeks 14-27) is often called the most comfortable stretch, as early symptoms fade and the fetus grows rapidly. The third trimester (weeks 28-40) is focused on continued growth and preparation for birth, with checkups typically becoming more frequent as the due date approaches.
Example — Your Current Inputs
With a last period starting July 9, 2026 and a 28-day cycle, conception most likely occurred around July 23, 2026, putting the estimated due date at April 15, 2027. As of today, that's 6 weeks and 0 days along — about 15.0% of the way through pregnancy, in the first trimester.
Additional Example — A Longer Cycle
Someone with a 35-day cycle and a last period on January 1 would have an estimated ovulation (and conception) date around January 22 — a week later than the "day 14" assumption used for a 28-day cycle. Their due date, however, is still October 8 either way, since Naegele's rule adds a fixed 280 days from the last period regardless of cycle length.
About These Parameters
- First Day of Last Period
- The starting point for every date in this calculator — due date, conception window, and trimester boundaries are all measured forward from this single date.
- Average Cycle Length
- Only affects the conception date estimate, not the due date. A longer-than-28-day cycle shifts the estimated conception date later; a shorter cycle shifts it earlier.
Frequently Asked Questions
Why does my due date use "40 weeks" if I wasn't pregnant for the first two?
Medical convention counts gestational age from the last menstrual period rather than conception, purely because LMP is a known date and conception rarely is. So the "40 weeks" figure includes about two weeks before you were actually pregnant.
How is this different from a Pregnancy Conception Calculator?
This calculator works forward from your last period to a due date and current progress. The Pregnancy Conception Calculator instead works backward — starting from a known due date or ultrasound to estimate when conception likely occurred.
Is an ultrasound more accurate than this calculation?
For most pregnancies, yes — a first-trimester ultrasound measuring the embryo directly is considered the most accurate dating method, especially if your cycles are irregular or you're unsure of your last period date.
What if I don't remember my exact last period date?
Use your best estimate — the calculation is only as precise as that input. If you're very unsure, an early ultrasound dating scan is the more reliable way to establish your due date.