Confidence Interval Calculator

Find the true score range for any special education test

Step 1: Pick Your Test

Select a common test below, or scroll down to enter values manually.

Test	Subtest / Composite	SEM

or enter your own values

Test Name (optional)

Auto-filled if you pick from the table

Standard Score

The score from the report

SEM

Standard Error of Measurement

Date Administered (optional)

If provided, this will appear on the downloaded image

Child's Name or Initials (optional)

For your records only

Step 2: Calculate

Confidence Level

95% CI 90% CI Reported Score

90% Confidence Interval

95% Confidence Interval

Calculated at decodingmom.com

When Confidence Intervals Do NOT Apply

CIs only work with standard scores from norm-referenced tests. They do not apply to:

Percentile ranks (non-linear scale; a 3-point difference at the 50th %ile is not the same as at the 2nd)
Criterion-referenced scores like CORE Phonics Survey (pass/fail by skill, no SEM)
CBM raw scores like DIBELS or easyCBM words correct per minute
Age or grade equivalents (these are ordinal, not interval-scaled)
Screener scores like iReady scale scores or MAP RIT (designed to sort, not diagnose)
Scores at the floor or ceiling of a test (SEM is unreliable at extremes)

If a school is using any of the above to argue your child "doesn't qualify," the confidence interval argument does not apply. Use other strategies from The Parent Investigator's Playbook.