How to Calculate Z-Score and Its Meaning

What Is Z-Rating?

Z-score is a statistical measurement that describes a price’s relationship to the imply of a gaggle of values. Z-score is measured when it comes to commonplace deviations from the imply. If a Z-score is 0, it signifies that the info level’s rating is similar to the imply rating. A Z-score of 1.0 would point out a price that’s one commonplace deviation from the imply. Z-scores could also be constructive or unfavourable, with a constructive worth indicating the rating is above the imply and a unfavourable rating indicating it’s beneath the imply.

In investing and buying and selling, Z-scores are measures of an instrument’s variability and can be utilized by merchants to assist decide volatility. The Z-score is typically confused with the Altman Z-score, which is calculated utilizing elements taken from an organization’s monetary stories. The Altman Z-score is used to calculate the chance {that a} enterprise will go bankrupt within the subsequent two years, whereas the Z-score can be utilized to find out how far a inventory’s return differs from it is common return and way more.

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  • A Z-Rating is a statistical measurement of a rating’s relationship to the imply in a gaggle of scores.
  • A Z-score can disclose to a dealer if a price is typical for a specified information set or whether it is atypical.
  • On the whole, a Z-score of -3.0 to three.0 suggests {that a} inventory is buying and selling inside three commonplace deviations of its imply.
  • Merchants have developed many strategies that use z-score to establish buying and selling positions, consider methods, and way more.

Z-Rating Method

The statistical method for a price’s z-score is calculated utilizing the next method:

z = ( x – μ ) / σ

The place:

  • z = Z-score
  • x = the worth being evaluated
  • μ = the imply
  • σ = the usual deviation

How To Calculate Z-Rating


Calculating a z-score requires that you just first decide the imply and commonplace deviation of your information. Upon getting these figures, you’ll be able to calculate your z-score. So, assume you’ve gotten the next variables:

You’ll use the variables within the method:

  • z = ( 57 – 52 ) / 4
  • z = 1.25

So, your chosen worth has a z-score that signifies it’s 1.25 commonplace deviations from the imply.


To find out z-score utilizing a spreadsheet, you may must enter your values and decide the typical for the vary and the stadard deviation. Utilizing the formulation:



You may discover that the next values have a imply of 12.17 and a typical deviation of 6.4.

1 Issue (x) Imply (μ) St. Dev. (σ)
2 3 12.17 6.4
3 13  12.17 6.4
4 12.17 6.4
5 21  12.17 6.4
6 17 12.17 6.4
7 11 12.17 6.4

Utilizing the Z-score method, you’ll be able to work out every issue’s z-score. Use the next method in D2, then D3, and so forth:

Cell D2 = ( A2 – B2 ) / C2

Cell D3 = ( A3 – B3 ) / C3

1 Issue (x) Imply (μ) St. Dev. (σ) Z-Rating 
2 3 12.17 6.4 -1.43
3 13  12.17 6.4 0.13
4 12.17 6.4 -0.65
5 21  12.17 6.4 1.38
6 17 12.17 6.4 0.75
7 11 12.17 6.4 -0.18

How To Use the Z-Rating

In it is most simple kind, the z-score permits you establish how far (measured in commonplace deviations) the returns for the inventory you are evaluating are from the imply of a pattern of shares. The common rating you’ve gotten could possibly be the imply of a inventory’s annual return, the typical return of the index it’s listed on, or the typical return of a number of shares you have picked.

Some merchants use the z-scores in additional superior evalulation strategies, similar to weighting every inventory’s return to make use of issue investing, the place shares are evaluated based mostly on particular attributes utilizing z-scores and commonplace deviation. Within the foreign exchange markets, merchants use z-scores and confidence limits to check the potential of a buying and selling system to generate successful and dropping streaks.

Z-Scores vs. Customary Deviation

In most giant information units (assuming a standard distribution of information), 99.7% of values lie between -3 and three commonplace deviations, 95% between -2 and a couple of commonplace deviations, and 68% between -1 and 1 commonplace deviations.

Customary deviation signifies the quantity of variability (or dispersion) inside a given information set. As an illustration, if a pattern of usually distributed information had a typical deviation of three.1, and one other had one in every of 6.3, the mannequin with a typical deviation (SD) of 6.3 is extra dispersed and would graph with a decrease peak than the pattern with an SD of three.1.

A distribution curve has unfavourable and constructive sides, so there are constructive and unfavourable commonplace deviations and z-scores. Nevertheless, this has no relevance to the worth itself aside from indicating which facet of the imply it’s on. A unfavourable worth means it’s on the left of the imply, and a constructive worth signifies it’s on the best.

The z-score reveals the variety of commonplace deviations a given information level lies from the imply. So, commonplace deviation have to be calculated first as a result of the z-score makes use of it to speak an information level’s variability.

How Is Z-Rating Utilized in Actual Life?

A z-score is utilized in many real-life purposes, similar to medical evaluations, check scoring, enterprise decision-making, and investing and buying and selling alternative measurements. Many merchants that use statistical measures like z-scores to judge buying and selling alternatives are referred to as quant merchants (quantitative merchants).

What Is a Good Z-Rating?

The upper (or decrease) a z-score is, the additional away from the imply the purpose is. This is not essentially good or dangerous; it merely reveals the place the info lies in a usually distributed pattern. This implies it comes all the way down to choice when evaluating an funding or alternative. For instance, some traders use a z-score vary of -3.0 to three.0 as a result of 99.7% of usually distributed information falls on this vary, whereas others may use -2.0 to 2.0.

Why Is Z-Rating So Necessary?

A z-score is vital as a result of it tells the place your information lies within the information distribution. For instance, if a z-score is 1.5, it’s 1.5 commonplace deviations away from the imply. As a result of 68% of your information lies inside one commonplace deviation (whether it is usually distributed), 1.5 is likely to be thought of too removed from common on your consolation.

The Backside Line

A z-score is a statistical measurement that tells you the way far-off from the imply (or common) your datum lies in a usually distributed pattern. At its most simple stage, traders and merchants use quantitative evaluation strategies similar to a z-score to find out how a inventory performs in comparison with different shares or its personal historic efficiency. In additional superior z-score makes use of, merchants weigh investments based mostly on fascinating standards, develop different indicators, and even attempt to predict the end result of a buying and selling technique.