IUD Pregnancy Risk Calculator

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Using an IUD is one of the most effective ways to prevent pregnancy, but risk isn’t zero—especially early after insertion or if the device has moved. This quick calculator uses IUD type, time since insertion, whether strings are felt, possible expulsion signs, and when intercourse happened to estimate your per-act risk and what to do next.

Early months carry a higher expulsion risk.

* Calendar dates cannot identify a safe day with an IUD. This is an approximate per-act estimate; strings and expulsion concerns need a position check, not reassurance from a low percentage. Use backup protection and seek advice if the IUD may have moved.

Peer-Reviewed Science
Updated Oct 2026
See Methodology
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Methodology & Sources

What this estimates

This calculator estimates an approximate pregnancy chance for one act of intercourse using the selected IUD type, time since insertion, strings check and signs of expulsion. It also gives guidance on checking the IUD's position and the timing of emergency contraception. Period dates do not change the estimated IUD risk; the intercourse date sets the emergency-contraception timing message.

Baseline effectiveness (IUDs)

Hormonal and copper IUDs have typical-use failure rates below 1% per year. These annual figures provide background on IUD effectiveness; they are different from the approximate chance for one act of intercourse shown here.

Sources: CDC: Contraception and Birth Control Methods; WHO: Intrauterine devices (IUDs), 2026.

Cycle dates and IUD protection

Period dates do not establish whether an IUD is providing protection. The calculator uses its IUD-type estimate without multiplying it by a predicted fertile-window factor. It does not infer a safe day from your last period. The intercourse date still sets the emergency-contraception timing message.

CDC guidance on intrauterine contraception addresses method use and clinical assessment. Calendar-day conception data from people not using contraception do not establish day-specific IUD failure risk.

Compromised-protection flags

We apply cautious multipliers (still bounded) when protection may be compromised:

  • Expulsion signs: suspected/likely expulsion increases risk (temporary multipliers) and triggers the warning box.
  • Strings not felt: treated as possible malposition until confirmed; we advise backup and a position check.
  • Very early post-insertion (first month): small additional risk due to higher expulsion risk shortly after placement.

Sources for clinical handling: CDC U.S. Selected Practice Recommendations (SPR) and ACOG LARC guidance (evaluation of missing strings/expulsion).

Emergency contraception window

The tool shows whether you are within an EC window based on the intercourse date:

  • Levonorgestrel (LNG) pills: most effective within 3 days (72 h) after intercourse.
  • Ulipristal acetate (UPA): up to 5 days (120 h) after intercourse.
  • Copper IUD as EC: the most effective EC when appropriate, typically up to 5 days after intercourse.

Sources: ACOG EC guidance; CDC SPR EC section.

Computation notes

  • Engine: Uses the selected IUD method without a cycle-day multiplier. The strings, expulsion and time-since-insertion adjustments are approximate; they do not measure the chance for a confirmed displacement or failure.
  • Bounds: Results are clamped to avoid unrealistic extremes and shown as a percentage with a qualitative band.
  • Flags: “Strings not felt” or expulsion signs raise the displayed risk band and show safety guidance.

Limitations

Population averages cannot reflect individual device position, insertion technique, postpartum status, medications, or clinic-specific practices. If you suspect expulsion or pregnancy symptoms, seek clinical assessment.

How to read your result

  • Lower risk: Strings felt, no expulsion signs, and several months since insertion.
  • Higher risk: Can’t feel strings, device or clots passed, severe cramps/bleeding, or very recent insertion.
  • Timing matters: If there are expulsion signs, seek advice promptly regardless of your predicted cycle day.

What to do now

  • Strings check: If you normally feel them and now can’t—or you suspect expulsion—use backup protection and contact a clinician.
  • Emergency window: If intercourse was within the last 120 hours (5 days), emergency contraception may help. A copper IUD placed within 5 days is the most effective EC; pills are another option.
  • Testing: If risk wasn’t negligible, plan a urine test on the first reliable day and repeat if negative and period is still late.
Heads-up: This tool provides estimates for a single encounter. It doesn’t diagnose expulsion or confirm correct placement—only an exam or imaging can do that.

FAQ

Do missing strings always mean the IUD failed?
Not always. Strings can curl into the cervix. But if you usually feel them and now can’t—or you have pain, heavy bleeding, or think the IUD passed—use backup protection and contact a clinician to check placement.
Is pregnancy risk higher right after insertion?
Insertion timing and early expulsion matter. Risk is still very low overall, but it’s prudent to use backup if expulsion is suspected in the first weeks after placement.
Does IUD type change risk?
Both copper and hormonal IUDs are highly effective. Differences in typical-use failure are small relative to expulsion or malposition issues—strings check and follow-up are more important drivers of risk.
What if intercourse was within the last 5 days?
You may still be in the emergency contraception window. A copper IUD placed within 5 days is the most effective EC; EC pills are another option. Plan your first reliable test day if pregnancy is possible.

Sources

Educational info only; not medical advice. For suspected expulsion or pregnancy symptoms, contact a clinician promptly.