Multiplicative Seasonal Index Calculator
Estimate normalized seasonal indices from complete cycles after removing each cycle mean.
YOUR CALCULATION
Result
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Calculation steps
Work through one step at a time or reveal the complete calculation. The steps use your current inputs.
How to calculate
Remove each complete cycle’s mean before averaging like seasonal positions.
Within-cycle ratio=value/cycle mean; seasonal index=phase mean ratios normalized to mean1
Worked example
Cycles10,20 and20,40 give phase indices2/3 and4/3.
Assumptions and input details
Complete cycles, at least two cycles, positive observations and stable within-cycle seasonal structure. This simple ratio-to-cycle-mean method does not separately estimate within-cycle trend or supply a forecast interval.
Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
Is my input uploaded?
The calculation runs in your browser. No account, file upload or external AI service is required. Inputs are not saved between page reloads.
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