IUI Due Date Calculator Guide
If you've conceived through IUI (intrauterine insemination), you may be wondering how to calculate your due date. While IUI dating is slightly different from IVF, the good news is that you likely know your conception timing with reasonable precision. This guide explains how to calculate your IUI due date and what makes it different from natural conception and IVF dating.
IUI at a Glance
What is IUI?
Intrauterine insemination (IUI) is a fertility treatment where prepared sperm is placed directly into the uterus around the time of ovulation. It's often called "artificial insemination" and is a less invasive option than IVF.
IUI is commonly used for:
- Unexplained infertility
- Mild male factor infertility
- Cervical factor issues
- Single women using donor sperm
- Same-sex couples
- Ovulation disorders (combined with ovulation induction medications)
Unlike IVF, fertilization in IUI happens inside your body, not in a laboratory. This affects how we calculate the due date.
The IUI Due Date Formula
For IUI, the due date is calculated based on when insemination occurred. The key date is your IUI procedure date, which serves as a proxy for the conception date.
The Basic Formula
Due Date = IUI Date + 266 days
Or equivalently: Due Date = IUI Date + 38 weeks
Why 266 Days?
A full-term pregnancy is 40 weeks (280 days) from the last menstrual period (LMP), or 38 weeks (266 days) from conception. Since IUI is performed at the time of ovulation (when conception would occur), we add 266 days—the time from conception to due date.
Alternative: Using Theoretical LMP
If you prefer to use standard pregnancy dating from LMP, calculate your theoretical LMP:
Theoretical LMP = IUI Date - 14 days
Then use a standard due date calculator with this date, which will give you the same result (IUI date + 266 days = theoretical LMP + 280 days).
IUI Due Date Calculation Examples
Example 1: Spring IUI
Your IUI was performed on March 20, 2026.
- IUI date: March 20, 2026
- Add 266 days (38 weeks)
- Due date: December 11, 2026
Theoretical LMP: March 20 - 14 = March 6, 2026
Example 2: Summer IUI
Your IUI was on July 15, 2026.
- IUI date: July 15, 2026
- Add 266 days
- Due date: April 7, 2027
Example 3: Fall IUI
Your IUI was on October 1, 2026.
- IUI date: October 1, 2026
- Add 266 days
- Due date: June 24, 2027
IUI vs. IVF: Comprehensive Comparison
Understanding how IUI compares to IVF helps clarify the differences in cost, invasiveness, success rates, and due date calculation methods.
| Factor | IUI | IVF |
|---|---|---|
| Procedure invasiveness | Minimally invasive (no surgery) | Invasive (egg retrieval under sedation) |
| Where fertilization occurs | Inside the body (fallopian tube) | In the laboratory |
| Success rate per cycle | 10-20% | 40-55% (under 35) |
| Average cost per cycle | $500-$4,000 | $12,000-$25,000 |
| Medication intensity | Low (oral or low-dose injectables) | High (daily injections for 10-14 days) |
| Monitoring visits per cycle | 2-4 visits | 5-8+ visits |
| Anesthesia required | ✗ | ✓ (for retrieval) |
| Genetic testing possible | ✗ | ✓ (PGT-A/PGT-M) |
| Due date formula | IUI date + 266 days | Transfer date + 260-263 days |
| Dating precision | Within 1-2 days | Exact to the day |
| Known date used | Insemination date | Embryo transfer date |
| Embryo age known at conception | ✗ (day 0 assumed) | ✓ (day 3, 5, or 6) |
Why IUI Dating is Slightly Less Precise
With IVF, we know the exact day of fertilization because it happens in the lab. With IUI, we place sperm in the uterus near the time of ovulation, but the exact moment of fertilization is unknown. Fertilization could occur the same day as IUI or 12-24 hours later when the egg is released and meets the sperm.
This creates a small margin of uncertainty (typically 1-2 days) that doesn't exist with IVF. However, IUI dating is still much more precise than natural conception dating based on LMP alone.
Types of IUI Cycles and Dating
The type of IUI cycle affects how precisely you can date your pregnancy:
Trigger Shot IUI (Most Precise)
If you received a trigger shot (hCG injection) to induce ovulation, your dating is most precise. The trigger shot causes ovulation approximately 36-40 hours later, and IUI is typically timed to coincide with this. You can be confident that ovulation occurred very close to your IUI date.
Natural Cycle IUI with OPK
If you used ovulation predictor kits (OPKs) to time your IUI, you likely ovulated within 24-36 hours of your positive test. IUI is usually performed the day after a positive OPK, which should align closely with ovulation.
Medicated Cycle with Monitoring
If you used ovulation-stimulating medications (like Clomid or letrozole) with ultrasound monitoring, your doctor tracked follicle development and timed the IUI accordingly. This provides good precision for dating purposes.
Calculating Gestational Age After IUI
To calculate your current gestational age from your IUI date:
- Count the days from your IUI date to today
- Add 14 days (to convert from conception age to gestational age)
- Divide by 7 to get weeks, with the remainder being extra days
Example
Your IUI was 42 days ago. What's your gestational age?
- Days since IUI: 42
- Add 14: 42 + 14 = 56 gestational days
- Divide by 7: 56 ÷ 7 = 8 weeks exactly
- Gestational age: 8 weeks, 0 days
IUI Pregnancy Milestones
IUI pregnancies follow the same milestone timeline as other pregnancies. Here are key dates relative to your IUI:
| Milestone | Gestational Age | Days After IUI |
|---|---|---|
| Positive pregnancy test | 4 weeks | ~14 days |
| First ultrasound | 6-7 weeks | 28-35 days |
| Heartbeat visible | 7 weeks | ~35 days |
| End of first trimester | 13 weeks | ~77 days |
| Anatomy scan | 18-22 weeks | 112-140 days |
| Viability | 24 weeks | ~154 days |
| Third trimester | 28 weeks | ~182 days |
| Full term | 37 weeks | ~245 days |
| Due date | 40 weeks | 266 days |
Ultrasound Dating vs. IUI Date
Like with all pregnancies, early ultrasounds will measure your baby to estimate gestational age. How does this compare to IUI-based dating?
First Trimester Ultrasound
Ultrasounds between 6-9 weeks are accurate to within 3-5 days. If your ultrasound dating closely matches your IUI-based dating (within a week), your provider will likely use the IUI date since it's a known reference point.
When Dates Don't Match
Small discrepancies (up to 5 days) are normal and don't usually change your due date. Larger discrepancies may indicate:
- Ovulation occurred slightly before or after the expected time
- Normal variation in early embryonic growth
- Ultrasound measurement variation
Your provider will determine the best dating approach based on all available information.
Using Pregnancy Apps and Medical Forms
Most pregnancy apps and medical forms ask for your LMP, not your IUI date. Here's how to handle this:
Calculate Your Theoretical LMP
Theoretical LMP = IUI Date - 14 days
Enter this date as your LMP, and the app or form will calculate your due date and gestational age correctly.
Example
IUI date: March 20, 2026
Theoretical LMP: March 20 - 14 = March 6, 2026
Entering March 6 as your LMP will give you the correct due date of December 11, 2026.
IUI Success and Multiple Pregnancies
IUI with fertility medications can increase the chance of multiples (twins, triplets) because medications may cause multiple eggs to be released. If you're pregnant with multiples after IUI, the due date calculation remains the same, but your expected delivery timing will be earlier (see our twins due date guide for more information).
What If I Don't Know My Exact IUI Date?
If you're unsure of your exact IUI date:
- Check your records: Your fertility clinic should have the exact date documented
- Check your calendar: You likely noted the appointment
- Use your trigger shot date: If you triggered, ovulation was about 36 hours later
- Use early ultrasound: If records aren't available, an early ultrasound can estimate gestational age
IUI Dating Accuracy Compared to Natural Conception
How does IUI dating compare to natural conception and IVF?
Most Accurate: IVF
With IVF, the fertilization date is known exactly because it occurs in the laboratory. The embryo age at transfer is precisely documented. Dating accuracy: exact to the day.
Very Accurate: IUI
The IUI date provides a close approximation of conception timing. Ovulation occurs within about 24 hours of the procedure. Dating accuracy: within 1-2 days.
Least Accurate: Natural Conception with LMP
LMP-based dating assumes ovulation on day 14, but actual ovulation timing varies significantly. Many women have irregular cycles. Dating accuracy: may be off by a week or more.
When Your Provider Might Adjust Your Due Date
Your provider may adjust your IUI-based due date if:
- Early ultrasound shows more than 7 days discrepancy from IUI dating
- There's uncertainty about the exact IUI date
- Ovulation timing was uncertain (no trigger shot, no monitoring)
In most cases with documented, monitored IUI cycles, the IUI-based date is reliable and won't need adjustment.
IUI Due Date Calculation Methods Compared
There are several ways to calculate your due date after IUI, depending on which information you have. All methods should give you the same (or very similar) result.
| Calculation Method | Formula | Example (IUI on March 20) | Precision |
|---|---|---|---|
| From IUI/insemination date | IUI date + 266 days | March 20 + 266 = December 11 | Within 1-2 days |
| From trigger shot date | Trigger date + 14 = theoretical LMP, then + 280 days | March 18 trigger + 14 = LMP March 4, + 280 = Dec 9 | Within 1-2 days |
| From LMP (theoretical) | (IUI date - 14 days) + 280 days | March 6 (theoretical LMP) + 280 = December 11 | Within 1-2 days |
| From actual LMP (if regular cycles) | LMP + 280 days | Varies; may be off if cycles are irregular | Within 1-14+ days |
| From early ultrasound (6-9 weeks) | CRL measurement estimates gestational age | Should confirm within 5 days of IUI-based date | Within 3-5 days |
The most straightforward method for IUI patients:
Due Date = IUI Date + 266 days (38 weeks)
This works because IUI is performed at the time of ovulation, which is approximately 14 days after the theoretical LMP. Since a full pregnancy is 280 days from LMP (or 266 days from conception/ovulation), adding 266 days to your IUI date gives you the same result as the standard pregnancy calculation.
For pregnancy apps that only accept LMP, use: Theoretical LMP = IUI Date - 14 days
IUI Success Rates by Age Group and Diagnosis
IUI success rates vary significantly based on maternal age and the underlying cause of infertility. These approximate per-cycle rates reflect IUI with ovulation stimulation medications.
Success Rates by Age
Success Rates by Diagnosis
Success rates are approximate and vary by clinic, medication protocol, and individual factors. Medicated IUI cycles typically have higher success rates than natural cycle IUI.
When to Move from IUI to IVF
IUI is often the first-line fertility treatment, but there are clear criteria for when patients and providers typically consider transitioning to IVF for better chances of success.
| Criteria | Typical Threshold | Reasoning |
|---|---|---|
| Number of failed IUI cycles | 3-6 cycles | Success rates plateau after 3-4 cycles; diminishing returns |
| Age | 38+ years | IUI success drops significantly; IVF offers better per-cycle rates |
| Severe male factor | Total motile count <5 million post-wash | Too few sperm for IUI to be effective; ICSI needed |
| Tubal disease | Both tubes blocked or damaged | IUI requires at least one open tube; IVF bypasses tubes entirely |
| Advanced endometriosis | Stage III-IV | IUI success rates very low; IVF significantly more effective |
| Need for genetic testing | Any case requiring PGT | Only IVF allows preimplantation genetic testing |
| Diminished ovarian reserve | Low AMH or high FSH | IVF can retrieve multiple eggs before further decline |
| Patient preference | Any time | Some patients prefer to move to higher-success treatment sooner |
Despite lower per-cycle success rates compared to IVF, IUI remains an important first-line treatment for many patients. It is less invasive, significantly less expensive, requires less medication and monitoring, and has minimal recovery time. Many patients conceive successfully through IUI without ever needing IVF. Cumulative success rates after 3-4 IUI cycles can reach 30-50% for appropriate candidates under 35.
Frequently Asked Questions
Can I use an IVF due date calculator for my IUI pregnancy?
Our IVF calculator is designed for embryo transfers with known embryo ages. For IUI, use the simpler formula: IUI date + 266 days. Alternatively, calculate your theoretical LMP (IUI date - 14 days) and use any standard due date calculator.
What if I had IUI on a different day than my positive OPK?
Use your IUI date, not your OPK date. The IUI date is when sperm was placed in your uterus, which is the closest approximation to conception timing.
I had back-to-back IUIs two days in a row. Which date do I use?
If you had two IUI procedures, use the date of the first IUI. Alternatively, use the midpoint between them. The difference of 1-2 days is within normal variation and won't significantly affect your due date.
Is my IUI due date as reliable as an IVF due date?
IUI dating is slightly less precise than IVF (within 1-2 days vs. exact), but it's still very reliable—much more so than natural conception LMP dating. Your due date should be accurate within a few days.
My IUI cycle was medicated. Does this affect the due date?
Medications like Clomid, letrozole, or gonadotropins don't change the due date formula. What matters is when ovulation occurred, which your provider timed the IUI to coincide with, regardless of what medications were used to stimulate ovulation.
Summary
Key points for calculating your IUI due date:
- Formula: IUI date + 266 days = Due date
- Theoretical LMP: IUI date - 14 days (for apps and forms)
- Accuracy: Within 1-2 days (more precise than natural conception)
- Gestational age: Days since IUI + 14, then divide by 7
- Same milestones: IUI pregnancies follow the same developmental timeline
- Ultrasound confirmation: Early ultrasound should closely match IUI-based dating
For IVF pregnancies with known embryo transfer dates, use our IVF Due Date Calculator for precise calculations. For IUI pregnancies, use the simple formula above or your theoretical LMP with a standard pregnancy calculator.
This article is for informational purposes only. Due dates are estimates. Always consult your healthcare provider for personalized guidance about your IUI pregnancy and dating.