Plan your frozen embryo transfer. Choose medicated or cryonatural, enter your next cycle start and embryo day (3/5), and we’ll estimate the transfer date, hormone-timing milestones, and your beta-hCG test day.
What the calculator does
- Estimates an embryo transfer date and key milestones for medicated (programmed) and cryonatural (natural/modified natural) cycles.
- Aligns transfer timing to the endometrium’s expected progesterone exposure so that a day-3 embryo is placed at about P+3 (or ovulation+3 in natural cycles), and a day-5 blastocyst at about P+5 (ovulation+5 in natural cycles).
How dates are generated (rules of thumb)
- Medicated cycle (no ovulation): model starts estrogen a few days after cycle start to prime the lining. Progesterone (“P day 0”) begins when the lining is ready; transfer is scheduled by embryo stage: day-3 → P+3; day-5 → P+5. The “beta” pregnancy test is set ~10 days after transfer.
- Cryonatural cycle: ovulation is estimated as cycle length − 14 days from period start (or by LH surge if known). That ovulation day is treated as the start of progesterone exposure. Transfer: day-3 → ovulation+3; day-5 → ovulation+5. Beta is ~10 days post-transfer.
- Small clinic-to-clinic shifts (e.g., blastocyst on P+5 or P+6; modified-natural using hCG trigger with transfer at ~hCG+7) are common. This tool chooses widely used targets and rounds to calendar days for clarity.
Scope & guardrails
- Educational planning only. Actual timing depends on ultrasound lining checks, progesterone start time, LH/hCG trigger timing in natural/modified-natural cycles, and lab scheduling.
- If your clinic specifies different “P+” or “LH+ / hCG+” targets, follow those instructions.
Sources
- Mackens S, Racca A, Van de Velde H, et al. Preparation of the endometrium for frozen embryo transfer: a systematic review. Front Endocrinol (Lausanne). 2021;12:688237. Practical timing: cleavage ~P+3; blastocyst ~P+5 in programmed HRT; natural-cycle blastocyst ~LH+6 (or ~hCG+7 if triggered). frontiersin.org/articles/10.3389/fendo.2021.688237/full
Last updated: 16 Oct 2025
How to use this calculator
- Select Medicated or Cryonatural (cycle type). For cryonatural, confirm your average cycle length.
- Enter your next cycle start date.
- Choose the embryo maturity (Day 3 or Day 5).
- Click Calculate to see your transfer date, hormone schedule, and beta-hCG test day.
Educational estimates only; timing varies by clinic protocol and clinical context.
What your results show
- Estimated transfer date — the target day for embryo placement.
- Hormone milestones — estrogen start (medicated) or LH surge/progesterone start (cryo).Protocol guide
- Beta-hCG test day — suggested clinic blood test date (~10 days after transfer).
- Countdown summary — days from today to your transfer.
Timing assumptions used
| Medicated cycle | ||
|---|---|---|
| Estrogen start | Start + 3 days | Or per clinic |
| Progesterone start | Estrogen + 12 days | +3 days if history of thin lining |
| Transfer (Day 3 embryo) | Estrogen + 16 days | +3 days if thin lining |
| Transfer (Day 5 embryo) | Estrogen + 18 days | +3 days if thin lining |
| Beta-hCG | Transfer + 10 days | Clinic may vary |
| Cryonatural cycle | ||
|---|---|---|
| Ovulation day | Cycle start + (cycle length − 14) | Assumes luteal ≈ 14 days |
| LH surge (approx.) | Ovulation − 2 days | Clinics confirm with OPKs/bloods |
| Progesterone start | Ovulation day | |
| Transfer (Day 3 embryo) | Ovulation + 3 days | |
| Transfer (Day 5 embryo) | Ovulation + 5 days | |
| Beta-hCG | Transfer + 10 days | |
These are pragmatic defaults to mirror common clinic windows; always follow your clinic’s instructions.
FET calculator: FAQs
How accurate are these dates?
They’re planning estimates. Clinics individualize protocols for lining response, prior cycles, medications, and monitoring. Use the results as a draft schedule to discuss with your team.
Day 3 vs Day 5 embryo—what changes?
Transfer is offset from progesterone/ovulation to match embryo developmental age. Day 5 embryos shift the transfer ~2 days later than Day 3 embryos.
What if I don’t know my exact cycle length (cryo)?
Leave the default at 28 days or use your average from the past few months. If you track LH/ovulation, use that to refine timing.
Thin lining—how does the tool adjust?
If you choose “Yes,” progesterone and transfer are pushed later to allow more estrogen exposure before luteal support begins.
When should I take a home pregnancy test?
Most clinics rely on a beta-hCG blood test about 10 days after transfer. Home urine tests can be misleading if taken early or after recent hCG trigger doses.