Due Date Calculator with Cycle Length
Adjust your due date for a cycle longer or shorter than 28 days.
Cycle-length adjusted due date — calculated locallyEstimates only — not medical advice. Confirm all dates and milestones with your doctor or midwife. Read our full disclaimer.
How this due date is calculated
Enter the first day of your last period and your usual cycle length. Longer or shorter cycles shift the due date by the difference from a 28-day cycle.
A longer or shorter cycle almost always means later or earlier ovulation, not a longer or shorter pregnancy. Ovulation is what starts the conception clock, and it typically arrives about 14 days before the next period — so a 35-day cycle ovulates near day 21 and pushes the due date about a week later than the 28-day default. This page adjusts only that ovulation shift, leaving the rest of the 280-day gestation untouched.
What to expect
The length of your whole cycle matters for dating only because it sets when you ovulate. Naegele's rule bakes in a 28-day cycle with ovulation near day 14; if your rhythm is different, ovulation — and therefore the conception clock — lands earlier or later, and the due date should follow.
The math is a single correction: due date = LMP + 280 days + (your cycle length − 28). A 32-day cycle adds 4 days; a 24-day cycle subtracts 4. Enter your usual length above and the shift is applied automatically, with no effect on the 280-day pregnancy itself.
Worked example: an LMP of March 5 with a steady 32-day cycle moves the due date from about December 10 to about December 14. The four-day nudge is exactly the gap between your cycle and the 28-day assumption — nothing more.
This lever is most useful when your cycles are regular but simply not 28 days. If the length jumps around each month, an ovulation predictor kit or an early ultrasound beats any single average, because it is your actual ovulation day that anchors the date.
A separate page on this site adjusts for luteal phase length — the post-ovulation window — which is a different measurement from total cycle length and is usually left at the default unless you have tracked it specifically.
Important note
These calculators use standard formulas — Naegele's rule (LMP + 280 days) and common IVF conventions (transfer date + 260–263 days). They give estimates for planning only. They are not a substitute for prenatal care, and only your provider can confirm your due date and track your baby's development. See the disclaimer for details.
FAQ
My cycle is 35 days — when did I ovulate?
With a 35-day cycle, ovulation typically lands around day 21 (about 14 days before your next period), roughly a week later than the 28-day default. This calculator shifts your due date later by that same 7 days, because later ovulation means a later conception clock.
Does a longer cycle mean a longer pregnancy?
No. A longer cycle means later ovulation, not a longer pregnancy. The time from ovulation to birth is about the same for everyone; only the LMP-based due date shifts, because the last period sits further from ovulation. The 280-day gestation itself is unchanged.
What if my cycle length changes every month?
This average adjustment assumes a regular cycle. If your length swings a lot month to month, an ovulation test or an early ultrasound gives a more reliable date than any single number you plug in here, since your real ovulation day is what matters.