Cost of Living Index Explained: What 100 Actually Means

Introduction

Every relocation comparison eventually produces the same number: a cost of living index where 100 is described as “average.” It is the most quoted figure in relocation planning and the most misread one.

An index of 100 does not mean a city is cheap, fair, or good value. It means that city was chosen as the reference point, and every other figure is measured against it. Understanding what sits behind that baseline is the difference between a relocation that saves money and one that quietly costs more than expected.

What the Index Actually Measures

A cost of living index is a weighted basket of everyday expenses. The typical weighting looks like this:

• Housing — usually the largest single weight, covering both rent and home prices
• Groceries — a standard basket of common food items
• Transportation — fuel, public transit fares, and vehicle costs
• Utilities — electricity, heating, water, and internet
• Healthcare — insurance premiums and out-of-pocket costs
• Goods and services — clothing, dining out, and personal care

Two cities can share the same headline index while the underlying basket looks completely different. A city where housing is expensive but groceries are cheap may land on the same total as one where housing is reasonable but utilities are punishing. The single number hides the trade-off.

Why 100 Is Only a Baseline

The value 100 is assigned to a reference location. Everything else is expressed relative to it, which you can write as:

index = (cost of the basket in your city / cost of the basket in the reference city) x 100

If your reference city is the national average and a city scores 120, that city is approximately 20% more expensive than the national average — for the basket as weighted, not for everything you buy.

Three practical consequences follow:

1. The reference point travels. An index built against a national average is not comparable with one built against a specific metro area. Always confirm what the baseline is.
2. Individual categories can diverge sharply. A city with an index of 115 might still have cheaper housing than a city at 105 if its other costs are higher.
3. Indices are periodic snapshots. Housing markets move faster than the basket is reweighted, so a published figure may lag current conditions.

How to Read a Score Correctly

The table is a reading aid rather than a threshold, and the boundaries are conventions rather than rules. Your personal index also depends on how you actually live: someone who rents will feel a housing-driven difference far more than someone who owns outright.

Applying the Index to Your Own Decision

An index compares baskets, not budgets. Three adjustments matter:

1. Replace the basket with your spending. If you will not own a car, the transportation weight in the index overstates your costs. If you have children, education costs may not be represented at all.
2. Compare against income, not just cost. A 120 index paired with salaries 40% above average can be more affordable than a 90 index paired with lower local wages. Our salary equivalence calculator converts one salary into its equivalent in another city.
3. Separate one-off from recurring costs. Moving expenses, deposits, and furnishing are paid once; rent and utilities recur every month. Our cost of living calculator handles the recurring side, while a one-time move needs its own break-even calculation.

Conclusion

A cost of living index is most useful as a first filter that narrows a long list of cities, not as a final answer. Read the baseline, look past the headline figure to the categories underneath, and translate it into your own salary and circumstances before making a decision.

Last updated: October 17, 2026