Irish Calculators
Saving & investing

Stock Beta Calculator from Paired Returns

Paste paired asset and benchmark returns for the same dates to estimate historical beta. The result measures past co-movement and does not forecast future risk.

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Your numbers

One row per matching period: YYYY-MM-DD, asset return %, benchmark return %. No headings. Use consistently adjusted returns.
Your figures stay on this device.

How the calculation works

Beta describes how an asset's returns moved alongside a benchmark in the observations you supply. It is a regression slope, not the asset's own volatility or the probability that its price will fall.

Beta = sum[(asset return − asset mean)(benchmark return − benchmark mean)] ÷ sum[(benchmark return − benchmark mean)²].

  1. Align the observations

    Only paired periods are meaningful. Prepare matching dates and return intervals before pasting; the calculator does not download or repair missing market data.

  2. Centre both return series

    Each observation is compared with its series mean. This removes the average level before measuring whether the asset and benchmark deviate together.

  3. Divide co-movement by benchmark variation

    The sum of paired deviations is divided by the benchmark's squared deviations. A benchmark with no variation cannot identify a slope, even if the asset varies.

Worked example: Check Historical beta

Sample inputs demonstrate the method. They are not a forecast or product offer.

In the first example, asset returns of 2%, 4% and 6% accompany benchmark returns of 1%, 2% and 3%. Every asset deviation is twice the corresponding benchmark deviation, so the fitted beta is 2.

Date, asset return %, benchmark return %
2026-01-01,2,1 2026-02-01,4,2 2026-03-01,6,3

Expected result

Historical beta
2
Worked example: Check Historical beta

Sample inputs demonstrate the method. They are not a forecast or product offer.

Date, asset return %, benchmark return %
2026-01-01,3,1 2026-02-01,2,2 2026-03-01,1,3

Expected result

Historical beta
-1

Understanding your result

A beta above one indicates a larger fitted response to benchmark changes in this dataset. A negative beta indicates an opposite fitted direction, not a guaranteed hedge.

The reported intercept is the fitted return when the benchmark return is zero for one observation period. Neither the slope nor intercept becomes an annual forecast merely because dates were entered.

Questions you might have

What does the result include?

Estimate historical beta from paired asset and benchmark returns for the same dates.

Which limits should I check?

Historical co-movement is not a forecast of future risk.

Choosing the right inputs

Date, asset return %, benchmark return %
Enter one date, asset return and benchmark return per row, without a heading. The date identifies the same observation period for both returns. Use percentages consistently and align dividend and split adjustments. A total-return asset series paired with a price-only benchmark changes the comparison.

Common mistakes to avoid

  • Do not paste price levels where the fields require returns.
  • Changing daily observations to monthly observations can change the estimate; keep the sampling basis consistent.

Assumptions to check

  • Historical co-movement is not a forecast of future risk.
  • All calculations run on your device. Figures are scenarios based on your inputs, not investment recommendations.

Sources and method

Read our calculation and testing approach.