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Weighted index number calculator

Work out

4 index numbers

4 weights

Weighted index number

106.1

Overall, after weighting, the total is 6.1% higher than in the base year.

Σ(index × weight)
10,610
Σweights
100

Working

  1. Multiply each index number by its weight: 108 × 30 = 3,240; 104 × 40 = 4,160; 112 × 20 = 2,240; 97 × 10 = 970.
  2. Add the products: Σ(index × weight) = 10,610.
  3. Add the weights: Σweights = 100.
  4. Weighted index number = 10,610 ÷ 100 = 106.1.

Your result

106.1. Overall, after weighting, the total is 6.1% higher than in the base year.

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Weighted index number = Σ(index × weight) ÷ Σweights: index numbers 108, 104, 112 and 97 with weights 30, 40, 20 and 10 give 10,610 ÷ 100 = 106.1.

Questions people ask

What is the weighted index number formula?

Multiply each item's index number by its weight, add the results and divide by the total of the weights: Σ(index × weight) ÷ Σweights. Indices of 108, 104, 112 and 97 with weights 30, 40, 20 and 10 give 10,610 ÷ 100 = 106.1.

What is a chain base index number?

It compares each period with the one just before it instead of with a fixed base year: this year ÷ last year × 100. A value of 96.3 means a 3.7% fall on the previous year.

What does an index number of 120 mean?

The value is 20% higher than in the base year, whose index is always 100. An index of 95 means 5% lower than the base year.

Why weight an index?

Not every item matters equally. A rise in rent affects a household far more than a rise in the price of salt, so each item counts in proportion to its weight, such as its share of spending.

Keep going

How we work this out

What it does

Work out a weighted index number, or fixed base and chain base index numbers for a series, with the steps shown.

Up to 20 items with index numbers and weights, or a series of up to 30 values for fixed base and chain base index numbers.

Method

  1. Index number = value ÷ base value × 100, so the base year is 100.
  2. Weighted index number = Σ(index × weight) ÷ Σweights.
  3. Chain base index number = this period's value ÷ last period's value × 100.