Endometrial Thickness Receptivity Calculator

Enter your ultrasound endometrial thickness in millimeters and choose the situation and timing you are in to get a plain-language, educational interpretation plus safety notes. This tool cannot diagnose problems or predict pregnancy, but it can help you ask better questions.

How to use our Endometrial Thickness Receptivity Calculator

1. Choose which situation fits you best (regular periods, IVF/FET planning, or postmenopausal).
2. Enter the endometrial thickness from your ultrasound report in millimeters (mm).
3. Pick how your timing is described (cycle day or progesterone days), then enter the day number.
4. If you selected a postmenopausal option, answer the bleeding question honestly (bleeding after menopause needs medical evaluation).
5. Open Advanced options if you can add details like usual cycle length, ovulation day, ultrasound type, fluid, or lining pattern.
6. Click Calculate and read the interpretation band and the typical range shown for your chosen timing.
7. If a safety flag appears, treat it as a priority message and contact a clinician promptly.
8. Use the suggested questions list to guide a call or appointment, and bring your full ultrasound report if you can.

Definitions

Endometrial thickness: The measured thickness of the uterine lining (endometrium) on ultrasound, usually reported in millimeters (mm).

Cycle day: The day of your menstrual cycle, where Day 1 is the first day of full-flow bleeding (not just spotting).

Ovulation day: The cycle day an egg is released (often estimated using an LH surge test).

Progesterone days: How many full days you have taken progesterone before the ultrasound in a planned treatment cycle.

Postmenopausal: After menopause, meaning you have not had a period for about 12 months (unless bleeding is from another cause).

Transvaginal ultrasound (TVUS): Ultrasound done with a probe in the vagina; it is often used for more precise lining measurements.

Fluid in the cavity: Fluid inside the uterus that can make a measurement harder to compare if it was included instead of excluded.

Trilaminar pattern: A three-layer look of the lining sometimes reported around ovulation; it is context only, not a guarantee.

Methodology

What this calculator does

This calculator gives an educational interpretation of an endometrial thickness number by matching it to the situation you selected (regular-cycle timing, embryo transfer planning, or postmenopausal context). It outputs (1) a plain-language interpretation band, (2) a typical reference range for the timing you entered, (3) whether your value is below/within/above that range, (4) a timing note about implantation, (5) safety flags, and (6) questions to ask your clinician.

Inputs and validation

Thickness must be a real number greater than 0 mm and at most 30 mm. Values outside that range are blocked because they are more likely to be a unit/report entry error (for example, cm typed as mm) or need immediate clinician review. Timing value must be provided when a timing type is chosen. Cycle day must be within a plausible range (error if less than 1 or very high). The postmenopausal bleeding question is shown only when you choose a postmenopausal context, so it cannot be accidentally ignored.

Cycle-phase timing (regular periods)

If you choose a regular-cycle context and enter a cycle day, the calculator classifies the day into a broad phase: Menstrual (days 1 to 4), Proliferative (days 5 to 13), Periovulatory (days 14 to 16), or Secretory (day 17 through your usual cycle length). If you enter an ovulation day in Advanced options, the calculator also computes days since ovulation as: days since ovulation = cycle day minus ovulation day. This helps explain timing (implantation is often discussed as occurring about 6 to 10 days after ovulation), but it is not turned into a pregnancy chance.

Transfer-planning context (IVF and FET)

If you select an IVF/FET-related option, the calculator uses a broad, educational reference band commonly used in clinics for lining checks (about 7 to 14 mm) and adds a timing note about progesterone exposure when progesterone days are provided. The tool does not assume a single correct schedule because clinics differ by protocol and embryo stage, so it frames this as a discussion prompt rather than a pass/fail score.

Postmenopausal safety triage

If you are postmenopausal and report bleeding, a safety flag is always shown advising prompt medical evaluation. Educationally, the tool also references the common TVUS threshold used in initial evaluation: endometrial thickness of 4 mm or less is considered a low-risk signal for endometrial cancer, but bleeding still needs evaluation and follow-up based on the full clinical picture [1]. If thickness is greater than 4 mm with postmenopausal bleeding, the calculator flags that as needing prompt evaluation [1].

Measurement-quality notes (to reduce mistakes)

If you report abdominal ultrasound instead of TVUS, the calculator adds a note that measurements may be less precise. If you report fluid in the uterine cavity, it adds a note that standard thickness measurement excludes fluid and the number may not be directly comparable to typical ranges. If a lining pattern (like trilaminar) is reported, the calculator treats it as context only and does not convert it into a guaranteed receptivity score.

Limits of what thickness can tell you

Endometrial thickness is only one piece of receptivity. Even when thickness is in a typical range, implantation depends on timing, hormones, uterine cavity factors, embryo factors (if relevant), and many other variables. Research in assisted reproduction shows thickness can correlate with outcomes in some settings, but it is not a perfect predictor and effects can plateau [3]. For ART populations, clinicians may also consider other risks and context beyond implantation alone [4].

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