P Value Calculator
Converts a z test statistic into a p-value for a left-tailed, right-tailed, or two-tailed test using the standard normal distribution, and flags significance at the 0.05 level.
What this calculator does
The P Value Calculator estimates your result instantly from the values you enter, using standard statistics formulas. Converts a z test statistic into a p-value for a left-tailed, right-tailed, or two-tailed test using the standard normal distribution, and flags significance at the 0.05 level. Calculations run in your browser, so nothing you type is sent to a server, and the output is an estimate rather than a certified or official figure.
Result
About P Value Calculator
This p-value calculator takes a z test statistic and returns the tail probability from the standard normal distribution. Pick two-tailed, left-tailed, or right-tailed and it applies the matching rule: left uses the cumulative area, right uses 1 minus that area, and two-tailed doubles the upper tail of the absolute z.
The result is capped between 0 and 1 and compared against α = 0.05 so you can see at a glance whether the outcome is significant.
Formula & Mathematical Calculation
P-Value = f(Test statistic (z), Test type)
Calculated according to standard stats formulas implemented in the calculator core.
Calculation Example
For z = 1.96 with a two-tailed test: p = 2 × (1 − Φ(1.96)) ≈ 0.05 (about 0.049996 to six decimals). Since this is below 0.05, the calculator marks it significant at α = 0.05.
Key Benefits
- Supports left-tailed, right-tailed, and two-tailed tests from a single z value
- Uses a standard normal approximation to return the p-value to six decimals
- Automatically states whether the result is significant at the 0.05 level
How to Use this Calculator
-
Enter the z statistic
Type your test statistic into the Test statistic (z) field, for example 1.96. -
Choose the test type
Select Two-tailed, Left-tailed, or Right-tailed from the Test type menu to match your hypothesis. -
Calculate
Select Calculate to see the p-value and whether it is significant at alpha = 0.05.
Assumptions & Limitations
What the calculation assumes
- Every value you enter is treated as an exact, known amount.
- Any rate or interval you enter is assumed to hold for the whole period unless the form asks for it separately.
- Results use standard published formulas and account only for the values entered above.
- Rounding is applied for display; the underlying calculation uses your full precision.
- Results are returned in the same units you enter, unless the tool states the output unit.
What it does not cover
- P Value Calculator produces a calculated result for reference and learning, not a certified or official measurement.
- Real-world outcomes differ when tolerances, rounding rules or local standards apply.
- Definitions and standards vary by region and change over time; verify the convention that applies to your case.
- Figures are only as accurate as the inputs you supply — check them before acting on the result.
- For work where the result carries real consequences, confirm it against an authoritative source.
Frequently Asked Questions
Free to use, no account needed. Calculations run in your browser, so nothing you type is sent to a server. Results are estimates — how we build and check our calculators.