Due Date Calculator with Luteal Phase
Fine-tune your due date using your luteal phase length.
Luteal-phase due date tweak — stays on your deviceEstimates 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 luteal phase length. A shorter or longer luteal phase shifts the due date slightly.
The luteal phase — the stretch from ovulation to the next period — is surprisingly stable for most people, usually 12–16 days, and largely independent of total cycle length. When it runs short (under about 10 days) it nudges the due date a few days later — a shorter luteal phase stretches the follicular phase that precedes it, so ovulation and conception fall later in the cycle — and can also signal something worth mentioning to your provider, since a weak luteal phase can affect early implantation. This calculator tweaks the date by the difference from the typical 14 days — a finer adjustment than the whole-cycle lever.
What to expect
The luteal phase is the stretch of your cycle after ovulation, running from egg release to the first day of the next period. Unlike total cycle length, it is remarkably steady for a given person — usually 12 to 16 days — and it barely moves when the overall cycle gets longer or shorter. That steadiness is exactly why it is worth a separate adjustment from the whole-cycle lever.
The tweak is small: due date = LMP + 280 days + (14 − your luteal phase length). A 12-day luteal phase pushes the date about 2 days later; an 18-day luteal phase pulls it about 4 days earlier. Most people never need to touch this, because 14 days is the common default.
Worked example: an LMP of May 9 with a tracked 11-day luteal phase gives a due date near February 4 rather than February 2. For someone charting basal temperature closely, that small shift reflects a real biological difference; for everyone else the default is fine.
One reason to know your luteal length: a consistently short phase (under about 10 days) can be a sign worth raising with your provider, since it may affect how well a pregnancy implants. The due-date effect is only a couple of days, but the signal itself matters more than the math.
This page pairs with the cycle-length calculator. Cycle length adjusts the whole rhythm; luteal phase adjusts only the post-ovulation window. Use whichever you have actually measured, not both, or the shift gets counted twice.
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
What is a normal luteal phase length?
Most people have a luteal phase of 12–16 days. It stays fairly constant from cycle to cycle and is largely independent of total cycle length, which is why it earns a separate adjustment from the whole-cycle lever on the cycle-length page.
Can a short luteal phase affect my due date?
A short luteal phase (under about 10 days) shifts the due date a few days earlier and can also be worth mentioning to your provider, since a weak luteal phase may affect how well an early pregnancy implants. The shift here is small but real — a couple of days, not weeks.
Luteal phase vs cycle length — which should I use?
Use cycle length if your whole cycle is longer or shorter than 28 days. Use luteal phase only if you have specifically tracked the post-ovulation window and found it differs from the usual 14 days. They adjust different parts of the same calculation, so applying both when only one applies would double-count the shift.