Editorial Policy

Last reviewed: June 2026 by the InvNorm Calculator Editorial Team. Report an issue

Content Accuracy

All content on InvNorm Calculator is written to be factually accurate and mathematically correct. Explanations, formulas, and worked examples are checked against established statistical references. Calculator results are validated through automated testing against known reference values.

Original Writing

Content on this site is original writing produced for InvNorm Calculator. We do not copy content from other sources. Mathematical definitions and formulas follow standard statistical conventions and are expressed in our own words and notation.

Review and Update Process

Content is reviewed periodically to ensure it remains accurate and up to date. Each page displays a "Last reviewed" date indicating when it was most recently checked. Reviews include:

• Verifying that mathematical explanations are correct and clearly written
• Confirming that calculator outputs match expected reference values
• Checking that links and references are still valid
• Updating content to reflect any improvements to the calculator

Correction Policy

If an error is identified in any content or calculation, we correct it as soon as possible. Significant corrections are noted on the affected page. If you find an error, please contact us so we can investigate and address it promptly.

Source Selection

Mathematical methods and algorithms used in this calculator are drawn from well-established, peer-reviewed sources. Our primary algorithm reference is Peter Acklam's rational approximation for the inverse normal CDF, which is widely cited in numerical computing. Supporting references include standard statistical textbooks such as Abramowitz and Stegun's Handbook of Mathematical Functions.

We do not cite sources that we have not reviewed, and we do not present unverified claims as established fact.

No Guaranteed Outcomes

This calculator is provided as an educational and analytical tool. While we make every effort to ensure accuracy, we do not guarantee that results are free from error. Users should verify important calculations independently, particularly when results will be used for academic submissions, professional decisions, or any context where accuracy is critical.

Calculator Testing Approach

The calculator's core mathematical functions are covered by automated unit tests that run against known reference values. These tests verify:

• The inverse CDF function produces correct Z scores for standard probabilities
• Boundary conditions (p = 0, p = 1) return appropriate results (NaN)
• All four probability modes (left, right, middle, two-tails) compute correct values
• Custom distributions with non-zero mean and non-unit standard deviation produce correct X values
• Input parsing handles percentages, decimals, and edge cases correctly

For details on the mathematical methods and their accuracy, see our methodology page.

Return to the InvNorm Calculator to run your own calculation.