IVF LMP-equivalent calculator
Build a paperwork LMP-equivalent from your IVF due date (roughly EDD − 280) so hospital forms and period apps stop inventing a period you never had. Estimate only — not medical advice.
Enter a transfer date to see an estimate.
What this page does
Hospital portals and pregnancy apps still ask for a last menstrual period even when you conceived through IVF and never had a relevant LMP. An LMP-equivalent is a paperwork date: roughly EDD minus 280 days, chosen so +280 apps land near your IVF due date.
It is not a claim that you menstruated that day. It is a translation layer for forms that refuse to speak transfer language. Think of it as a compatibility shim — like entering a date the software understands so it stops inventing a week of fiction.
You can start from a clinic EDD you already trust, or from transfer dating that first produces an EDD and then subtracts 280. Either way, the output is synthetic on purpose. If your clinic updates the EDD after a dating scan, rebuild the LMP-equivalent; do not keep an old fake period attached to an obsolete due date.
When to use
A hospital questionnaire will not submit without an LMP. A leave form or registry wizard only understands period dating. You want your partner's tracker app to stop being a week off.
Also useful when a nurse says "just put an LMP" and you want the arithmetic that matches your EDD — not a random date from a period three years ago. FET patients hit this wall constantly because consumer apps still assume spontaneous cycles.
When not to
Do not treat LMP-equivalent as proof of when a period happened. Do not use it to rewrite a dating ultrasound. If you have a real spontaneous LMP for a non-IVF pregnancy, use that real date instead of this tool.
Do not enter an old period "just to fill the box" and then wonder why every week count looks wrong. That is how charts desync.
Assumptions
Default: LMP-equivalent ≈ EDD − 280 days.
If you start from transfer dating, we first estimate EDD with the day-age offsets (Day 3/5/6), then subtract 280. We do not invent custom cycle-length variants on this page. Some clinics compute LMP-equivalent with slightly different conventions — match your clinic when the form is official medical record, not a consumer app.
Examples
EDD November 26, 2026 → LMP-equivalent February 19, 2026. November 26 − 280 days.
Day 5 transfer March 10, 2026 → EDD Nov 26, 2026 → LMP-eq Feb 19, 2026. Transfer path then −280.
EDD June 1, 2027 → LMP-equivalent August 25, 2026. Still a paperwork date, not a remembered period.
Gotchas
LMP-equivalent is for forms and incompatible apps — not a fertility memoir.
If two systems use different EDD anchors, their LMP-equivalents will disagree; fix the EDD first.
Some clinics compute LMP-equivalent with slightly different conventions; match your clinic when it matters for records.
Entering a real period from years ago "just to fill the box" will desync everything.
Rebuilding after a scan-updated EDD is required; stale LMP-equivalents quietly poison week counts.
This does not prove ovulation or menses occurred on that calendar day.
How this is calculated
Paperwork translation, not biology cosplay.
Prefer the clinic EDD when you have it. Transfer path is for when the EDD is not handy yet but the transfer label is. Either path should end in a date you knowingly treat as synthetic.
- Prefer entering the clinic EDD if you already have one.
- Or enter transfer date plus embryo age to derive EDD first.
- Read the LMP-equivalent (EDD − 280).
- Paste that date into forms that demand LMP — knowing it is synthetic.
- If the clinic updates EDD after a scan, rebuild the LMP-equivalent.
- Do not mix this fake LMP with a real remembered period from another time in your life.
LMP-equivalent ≈ EDD − 280 (EDD may come from transfer + (266 − age))
Related calculators
Reverse due date works backward from EDD to a conception window and also surfaces an LMP estimate — useful when the question is "when did things start?" This page is specifically about feeding an LMP field without lying to yourself about biology.
Forward IVF and FET dating remain the better source of the EDD whenever you still have transfer day. Build the LMP-equivalent after you trust that EDD.
See also: ivf due date calculator, fet due date calculator, and reverse due date calculator.
FAQ
- What is an IVF LMP equivalent?
- A synthetic last-period date, usually EDD minus 280 days, so LMP-based forms and apps align with your IVF due date. It is compatibility math, not a diary entry.
- Did I actually get my period on that day?
- Not necessarily — and often no. The date exists so software that only understands LMP dating can land near the correct EDD.
- Should I put this on medical records?
- Follow clinic instructions. Many IVF charts already store transfer dating; use LMP-equivalent when a form still demands it. If the clinic already printed their own LMP-equivalent, prefer theirs for official records.
- How does this relate to Day 5 +261?
- Transfer math produces an EDD; LMP-equivalent is just EDD − 280 for paperwork. You do not enter +261 into an LMP field — you enter the translated date.
- Can reverse dating replace this?
- Reverse dating emphasizes conception window and LMP estimate from EDD. Use this page when the job is specifically "feed an LMP field" and you want that framing front and center.
- Why 280 days?
- It matches the common LMP-to-EDD shortcut many apps use (about forty weeks). Pairing EDD − 280 with those apps is why the shim works.
- My app is still a few days off — why?
- Cycle-length defaults, time zones treated as clock time, or a different EDD anchor can nudge results. Align the EDD first, then rebuild the LMP-equivalent.
- Is this medical advice?
- No — estimate only for planning and forms.