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
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.