IUI Due Date Calculator: How to Calculate Your Due Date After IUI
By Emily Johnson, Content Writer & Fertility Advocate · Medically reviewed by Dr. Sarah Ahmed, Medical Content Advisor
Table of Content
Table of Contents
If you conceived with intrauterine insemination, an IUI due date calculator gives you a fast, reliable estimate of when your baby is due. Because your clinic timed the procedure to ovulation and documented the exact date, IUI dating is more precise than dating from your last period. This guide explains the formula, walks through worked examples, and answers the questions patients ask most.
How the IUI Due Date Calculator Works
The IUI due date calculator uses one simple formula:
Estimated due date = IUI procedure date + 266 days (38 weeks)
The 266-day count is the average length of pregnancy measured from fertilization. IUI earns its place in this formula through its timing: the procedure is performed about 24–36 hours after an hCG trigger shot, or within roughly a day of a detected LH surge, placing washed sperm in the uterus just as the egg is released. Fertilization follows within hours, so the IUI date and the true conception date are rarely more than a day apart.
That precision is also why IUI dating usually beats period-based dating for the same patient. The standard period method assumes ovulation on cycle day 14, but a monitored IUI cycle might have triggered on day 12 or day 18.
Two related dates fall out of the same calculation: your theoretical last menstrual period (LMP) is the IUI date minus 14 days, and your gestational age on IUI day is 2 weeks, 0 days. That is why you are already considered two weeks pregnant on the day of the procedure, even though fertilization has only just happened.
If you had more than one IUI cycle, always use the date of the cycle that led to this pregnancy — not an earlier one.
Worked Examples: Calculate Your IUI Due Date
Apply the IUI due date calculator formula to your own date with these two examples:
Example 1. Your IUI was performed on Tuesday, March 10, 2026. Add 266 days and your estimated due date is Tuesday, December 1, 2026. Your theoretical LMP is February 24, 2026, with a beta test around March 24.
Example 2. Your IUI was performed on Monday, June 15, 2026. Add 266 days and your estimated due date is Monday, March 8, 2027. Your theoretical LMP is June 1, 2026.
Check it against your period method. Suppose your last period began February 24, 2026, with a 28-day cycle. The classic Naegele’s rule calculation (LMP + 280 days) gives December 1, 2026 — the same date as Example 1. When the two methods agree, that agreement is reassuring.
IUI Due Date vs. IVF, LMP, and Ultrasound Dating
Every dating method answers the same question — when will you reach 40 weeks? — but each starts from a different known fact:
| Method | Starting point | Formula |
|---|---|---|
| IUI | Procedure date (timed to ovulation) | IUI date + 266 days |
| IVF Day 3 transfer | Embryo transfer date | Transfer date + 263 days |
| IVF Day 5 transfer | Embryo transfer date | Transfer date + 261 days |
| Last period (LMP) | First day of last period | LMP + 280 days |
| Ultrasound | Scan date + measured gestational age | Scan date + days remaining to 40 weeks |
IVF dating is the most precise of all, because both the transfer date and the embryo’s age are documented (see our IVF due date guide for 5-day transfer). IUI dating sits just behind it. LMP dating is the least precise, because it assumes ovulation on day 14.
Does the hCG Trigger Shot Change Your Due Date?
No. The trigger shot only times ovulation — typically 24–36 hours after the injection — so the insemination lines up with egg release. It does not change the due-date math, and you should still calculate from the IUI procedure date, not the trigger date.
The trigger shot does matter for one thing: pregnancy testing. It contains hCG, the same hormone home pregnancy tests detect, and it can cause a false positive for roughly 10–14 days after the injection. That is why clinics ask you to wait for the scheduled beta test, about 14 days after IUI. Our early pregnancy test calculator and beta hCG doubling calculator explain what those early numbers mean.
Special Cases: Back-to-Back IUIs, Donor Sperm, and Twins
Two IUIs on back-to-back days. Some clinics perform insemination on two consecutive days to cover the ovulation window. Use the first IUI date. Sperm from the first procedure can survive several days waiting for the egg, and the difference would only be 24 hours.
Donor sperm IUI. The calculation is identical — the source of the sperm does not change the timing.
Medicated vs. natural-cycle IUI. The formula is the same either way. Medicated cycles are often dated slightly more reliably, because follicle monitoring and the trigger shot pin down ovulation more tightly — but the math does not change.
Twins after IUI. The calculated 40-week due date stays the same, but multiples are almost always delivered earlier, typically around 36–38 weeks. See our guide to how many weeks pregnant you are after embryo transfer for how tracking works once pregnancy is confirmed.
When Your Due Date Can Change After IUI
A due date is an estimate, not an appointment: only about 1 in 20 babies arrives on the exact date. Your provider may formally revise the date in a few situations:
- First-trimester ultrasound differs by more than 5–7 days. The scan measurement usually wins, per guidance from the American College of Obstetricians and Gynecologists (ACOG).
- Your LMP was uncertain or irregular. If your cycle dates were unclear, the IUI and ultrasound dates carry more weight than the period-based estimate.
- Growth scans later in pregnancy suggest a different pattern. Later scans are less precise for dating, so providers are cautious about redating after the first trimester.
None of these changes mean the original calculation was wrong — each method is an estimate built on different information. The American Society for Reproductive Medicine (ASRM) offers patient resources on fertility treatment timelines. As always, confirm any change with your clinic before updating your own records.
Your Timeline After IUI: From the Two-Week Wait to the First Ultrasound
Using Example 1 (IUI March 10, 2026) as a reference, here is what the calendar typically looks like:
- Days 1–14 — the two-week wait. Implantation usually happens about 6–12 days after IUI. Avoid home testing early: leftover trigger-shot hCG can produce a false positive.
- Around day 14 (March 24) — beta hCG blood test. This is the first reliable confirmation. A second beta 48 hours later checks whether the level is rising as expected.
- Weeks 6–8 (April 21 – May 5) — first ultrasound. The dating scan confirms the heartbeat, measures the embryo, and locks in (or adjusts) the official due date.
- Weeks 8–12 — first-trimester screening. Blood work and the nuchal translucency scan are scheduled by gestational age.
- Week 40 (December 1) — estimated due date. Full term runs 37–42 weeks, so a healthy delivery anywhere in that window is normal.
Frequently Asked Questions
How accurate is the IUI due date calculator?
It is one of the more accurate starting estimates, because it is built on a documented procedure date timed to ovulation. Still, it is an estimate: implantation timing varies, and only about 5% of babies arrive on the exact due date. Your first-trimester ultrasound confirms or fine-tunes it.
Can I use an IUI due date calculator for a medicated cycle?
Yes. Medicated and natural-cycle IUI use the same formula — procedure date plus 266 days. Medicated cycles may be dated slightly more reliably.
I had two IUIs on back-to-back days. Which date do I use?
Use the first IUI date. Sperm from the first procedure can survive several days, and the difference would only be 24 hours.
Will my due date change after my ultrasound?
Possibly. If a first-trimester scan differs from the IUI-based date by more than about 5–7 days, your provider will usually adopt the ultrasound date. Redating after the first trimester is uncommon.
Does a twin pregnancy change the calculated due date?
No — the 40-week calculation is the same. Twins are simply usually delivered earlier, around 36–38 weeks.
About the author
Emily Johnson is a Content Writer & Fertility Advocate who covers IVF and fertility treatment topics. Meet the team
Medical review
This article was medically reviewed by Dr. Sarah Ahmed, Medical Content Advisor, for clinical accuracy. Meet the team
Medical disclaimer
This article is for informational purposes only and is not medical advice, diagnosis, or treatment. Due dates are estimates, and every pregnancy is different. Always confirm your due date and any testing or treatment decisions with your clinic or healthcare provider.
