Find your estimated conception date from your due date, ovulation date, or last menstrual period. Explore fertility windows and conception probability.
Conception Mode
Conception is estimated as due date minus 266 days (38 weeks).
Conception typically occurs on ovulation day or within 1-2 days prior.
Ovulation = LMP + (cycle length minus luteal phase).
Estimated Conception Date
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Enter a date above to calculate
Ovulation Est.
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Fertility Window
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Estimated Due Date
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Zodiac Sign
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Next Fertile Window
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Days Since Conc.
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Cycle Phase Visualization
Conception = Due Date − 266 daysOvulation = LMP + (cycle − luteal)Due Date = Ovulation + 266 days
Pregnancy Progress
Current Gestational Age
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Calculate above to see progress
Days Pregnant
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Days Remaining
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% Complete
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ConceptionT1T2T3Due Date
These are estimates. Actual conception depends on many biological factors. Confirm with your healthcare provider.
Fertile Window Calendar
The 6-day fertile window includes the 5 days before ovulation and ovulation day itself. Peak fertility is on the 1-2 days before ovulation.
MenstrualFollicularFertilePeak / OvulationLuteal
Fertile Window Timeline
Tracking Method Comparison
Compare different methods for identifying your fertile window.
📅
Calendar (Rhythm)
Accuracy: ~75%
Predicts ovulation based on average cycle length. Simple but less reliable for irregular cycles.
+ No equipment needed
+ Easy to track
− Assumes regular cycles
− Cannot confirm ovulation
🌡
BBT (Basal Body Temp)
Accuracy: ~85%
Tracks the 0.2-0.5 degree F rise in resting temperature after ovulation occurs.
+ Confirms ovulation occurred
+ Low cost
− Only detects AFTER ovulation
− Illness/sleep disrupts readings
🧪
OPK (Ovulation Kit)
Accuracy: ~97%
Detects LH surge 24-36 hours before ovulation. The gold standard for timing.
+ Predicts ovulation in advance
+ Very accurate
− Monthly cost for test strips
− PCOS can cause false positives
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Cervical Mucus
Accuracy: ~80%
Monitors changes in cervical fluid from dry to egg-white consistency near ovulation.
+ Free and natural
+ Real-time fertility sign
− Subjective interpretation
− Medications can alter mucus
Day-by-Day Fertility Data
Day
Date
Phase
Conception Probability
Probability by Day Relative to Ovulation
Research shows that conception probability varies significantly by the day intercourse occurs relative to ovulation. The highest chances are on O-1 and O-2.
Age-Adjusted Conception Rates
Your age group: 25-29. Monthly and cumulative conception rates decrease with age.
Per-Cycle Probability
25%
with well-timed intercourse
After 3 Months
58%
After 6 Months
82%
After 12 Months
96%
Cumulative Probability Over 12 Months
Tips for Maximizing Conception Chances
1
Time Intercourse to O-2 and O-1
The two days before ovulation have the highest conception probability (27% and 31% respectively). Start trying from 3 days before expected ovulation.
2
Every 1-2 Days During Fertile Window
Daily or every-other-day intercourse during the 6-day fertile window ensures sperm are present when the egg releases.
3
Use Multiple Tracking Methods
Combine calendar tracking with OPK tests and cervical mucus observation for the most accurate fertile window prediction.
4
Start Preconception Health Early
Begin folic acid (400-800mcg daily) at least 1 month before trying. Maintain a healthy BMI, limit alcohol, and manage stress.
5
Know When to Seek Help
Under 35: consult after 12 months. Age 35-39: after 6 months. Over 40: consult before or when you start trying.
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Lifestyle Factors Matter
Both partners should avoid excessive heat exposure, smoking, and heavy caffeine. Moderate exercise and adequate sleep support fertility.
The release of a mature egg from the ovary, typically occurring once per cycle around day 14 of a 28-day cycle.
Fertile Window
The approximately 6-day period when conception is possible: 5 days before ovulation through ovulation day.
LMP
Last Menstrual Period — the first day of the most recent period, used as the starting point for cycle calculations.
Luteal Phase
The post-ovulation phase lasting about 14 days. A short luteal phase (under 10 days) may affect implantation.
LH Surge
A rapid increase in luteinizing hormone that triggers ovulation, detectable by OPK tests 24-36 hours before egg release.
Basal Body Temperature
Your lowest body temperature at rest, which rises 0.2-0.5°F after ovulation due to progesterone.
Real-World Examples
Example 1
Regular 28-Day Cycle
LMP: March 1, Cycle length: 28 days, Luteal: 14 days
Result: Ovulation March 15. Fertile window: March 10-15. Peak days: March 13-14.
Example 2
Longer 35-Day Cycle
LMP: March 1, Cycle length: 35 days, Luteal: 14 days
Result: Ovulation March 22. Fertile window: March 17-22. Ovulation shifts later with longer cycles.
Example 3
From Due Date
Due date: December 15, 2026
Result: Estimated conception: March 24, 2026. That is 266 days before the due date.
Understanding Your Fertile Window
Timing Is Everything
Conception is only possible during about 6 days per cycle. The highest probability is the 2 days before ovulation and the day of ovulation itself. Having intercourse every 1-2 days during the fertile window maximizes chances.
Cycle Length Variation
Not everyone has a 28-day cycle, and ovulation does not always happen on day 14. If your cycle is 35 days, ovulation is likely around day 21. Tracking basal body temperature and cervical mucus can help pinpoint your personal pattern.
Age and Fertility
Female fertility peaks in the mid-20s and gradually declines after 30, with a steeper decline after 35. At 25, the per-cycle probability of conception is about 25-30%. By 35 it drops to about 15%, and by 40 to about 5-8%. Male fertility also declines with age, though more gradually.
When to Seek Help
If you are under 35 and have not conceived after 12 months of well-timed intercourse, consult a fertility specialist. Over 35, seek help after 6 months. Over 40, consider consulting before or right when you start trying.
Frequently Asked Questions
Can I know the exact date of conception?
The exact date of conception is rarely known with certainty. Sperm can survive inside the body for up to 5 days, and the egg is viable for 12-24 hours after ovulation. Conception could occur on any day within that window. The best estimate is ovulation day, since most conceptions occur on ovulation day or the day before.
How does cycle length affect conception timing?
In longer cycles, ovulation occurs later. For a 35-day cycle, ovulation is likely around day 21 (not day 14). The fertile window shifts accordingly. The luteal phase (post-ovulation) typically stays constant at 12-14 days regardless of cycle length. Only the follicular phase (pre-ovulation) varies.
Is the conception date the same as the ovulation date?
They are very close but not always identical. Conception (fertilization) occurs when sperm meets the egg, which happens in the fallopian tube within 12-24 hours of ovulation. If intercourse occurred days before ovulation, sperm may have been waiting in the reproductive tract. Clinically, conception date and ovulation date are treated as the same for calculation purposes.
Why is my conception date different from what my doctor calculated?
Doctors often use ultrasound measurements to date a pregnancy, which is more accurate than LMP-based calculations. If your cycle was irregular or you ovulated earlier or later than expected, the ultrasound-based conception date may differ from an LMP estimate by a week or more. The ultrasound measurement is generally more reliable.
What days have the highest chance of conception?
The day before ovulation (O-1) has the highest per-day conception rate at about 31%, followed by two days before ovulation (O-2) at about 27%. Ovulation day itself is around 10% because the egg has a limited 12-24 hour viability window. The combined 6-day fertile window gives the best overall chances.
Does age really affect conception probability?
Yes, significantly. Women under 25 have approximately a 25-30% chance per cycle. This drops to about 20% at 30-34, 15% at 35-39, and 5-8% after 40. These rates assume well-timed intercourse during the fertile window. Egg quality and quantity both decline with age, which is the primary factor.