Enter any of the three dates below, the other two update instantly, along with total pregnancy length and every key milestone
| Milestone | Gestational age | Date |
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| What you're finding | Formula | Value |
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Founder & CEO, Toolraxy
Faiq Ur Rahman is a web designer, digital product developer, and founder of Toolraxy, a growing platform of web-based calculators and utility tools. He specializes in building structured, user-friendly tools focused on health, finance, productivity, and everyday problem-solving.
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Most pregnancy date calculators go one way. You enter an LMP or a scan measurement and get a due date. This one runs the math in reverse too. Enter the due date your provider gave you, and it back-calculates a conception date, an intercourse window, and an LMP. Enter a conception date, and the due date resolves from that. Type in an intercourse date, and the tool fills in the rest.
That flexibility matters when you already know one piece of the puzzle. A clinic hands you a due date at your first appointment. You remember the weekend you conceived. You’re working out whether a specific encounter could have led to the pregnancy. Any of those starting points produces a complete set of dates in one step.
The calculator also shows pregnancy length from two anchors, tracks milestones across all 40 weeks, and counts down the days remaining. Nothing you enter leaves your browser.
Enter any one of three dates: due date, conception date, or intercourse date. The tool updates the others.
Set your average cycle length. The range is 20 to 45 days, default 28.
Adjust the “calculate as of” date if you want results for a future or past day. Today is the default.
Read the hero panel. Pregnancy length appears from both LMP and conception.
Check the context row for the resolved due date, conception date, and intercourse date.
Scan the four tiles for LMP, conception, intercourse, and the countdown.
Follow the gauge to see where you sit across the 42-week timeline.
Scroll the milestone table for dated events from LMP through post-term.
Every date in this tool derives from the same fixed anchor: the 280-day interval from LMP to due date.
Formula: LMP = due date − 280 days
That’s the only fixed constant. Everything else adjusts based on your cycle length.
Formula: Conception = due date − (294 − cycle length)
For a 28-day cycle, that’s 266 days before the due date. For a 35-day cycle, it’s 259 days before. The 294 figure exists because the standard 40-week count starts 14 days before conception, and cycle length shifts where that 14-day offset lands.
Formula: Intercourse date ≈ conception − 2 days
The two-day offset reflects the typical relationship between intercourse and fertilization, since sperm survive in the reproductive tract for up to five days but conception usually happens on the day of ovulation or within 24 hours.
Formula: Pregnancy length (from conception) = 294 − cycle length
A 28-day cycle gives 266 days. A 35-day cycle gives 259. That’s why conception-to-birth length varies between women while LMP-to-birth stays fixed at 280 days.
Cycle length is clamped between 20 and 45 days. The tool flags any input outside that range rather than producing a nonsensical result.
Say your provider gave you a due date of November 20, 2026, and your cycles average 30 days. You want to know when you conceived and roughly which intercourse window led to the pregnancy.
Due date: November 20, 2026
Cycle length: 30 days
Conception offset = 294 − 30 = 264 days
Conception date = November 20 − 264 days = March 1, 2026
Intercourse date ≈ March 1 − 2 days = February 27, 2026
LMP = November 20 − 280 days = February 13, 2026
Pregnancy length from LMP: 280 days (40 weeks 0 days)
Pregnancy length from conception: 264 days (37 weeks 5 days)
The calculator would show “40 weeks 0 days” in the hero, with the subtext confirming 280 days from LMP and 264 from conception. The tiles would show February 13, 2026 as your LMP, March 1 as conception, and February 27 as the estimated intercourse date. The countdown would update based on today’s date.
Try the same due date with a 35-day cycle. Conception shifts to February 24, and the intercourse window to February 22. That’s a full week earlier than with the 30-day cycle, which is why entering your real average matters.
Subtract (294 − cycle length) days from the due date. For a 28-day cycle, that’s 266 days. For a 35-day cycle, it’s 259 days. The result is an estimate, since ovulation timing varies.
Yes, but only as an estimate. The calculation assumes ovulation on the standard cycle day for your cycle length. Tracking ovulation with an OPK or BBT chart gives a more accurate conception date.
It’s the least precise of the three dates. It assumes intercourse happened two days before conception, which matches the population average. Intercourse up to five days before ovulation can also lead to pregnancy.
Conception is the moment of fertilization. Intercourse is when sex happened. Sperm can survive up to five days, so intercourse often occurs several days before conception.
A longer cycle pushes conception later relative to the due date, while the 40-week LMP count stays fixed. A 35-day cycle puts conception about a week later than a 28-day cycle.
The LMP-to-due-date count includes about two weeks before ovulation. Clinical dating starts from the LMP because it’s observable, while ovulation happens silently. Conception-to-birth length is 266 days in a 28-day cycle.
You don’t need it. The calculator derives the LMP from whichever date you enter. The equivalent LMP is what you’d report to a clinic that asks for it, and it appears in the tile row.
Yes, often by a few days. Ovulation timing varies between cycles, and the intercourse-to-conception window spans several days. An early ultrasound is more reliable than a reverse calculation for dating a pregnancy.
Not accurately. IVF uses the embryo’s age at transfer rather than a standard ovulation offset. Use an IVF-specific due date calculator or ask your clinic for the equivalent LMP they’re using.
It sets the reference point for gestational age and countdown. Today is the default. Change it to see how far along you were on a past date or will be on a future one.
It’s the total expected duration from either LMP or conception to the estimated due date. The LMP figure is always 280 days. The conception figure is 294 − cycle length.
Use it when you already have a due date, conception date, or intercourse date and want the others. A standard calculator works forward from an LMP or scan.
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