01
Paste your data
Put periods in the first column and each series in its own column. CSV and spreadsheet paste both work.
Free index to 100 calculator
Rebase time-series data to 100 online.
Paste CSV or spreadsheet data, choose a shared base period, and compare relative performance on one scale. Preview the indexed chart, download the transformed data, or continue into a publication-ready visual—free and without an account.
Runs in your browserCSV downloadNo sign-in
02
Choose the baseline
Select one non-zero period shared by every series. Each line will equal 100 there.
03
Export or publish
Download the indexed CSV or continue with source notes, annotations, and chart exports.
Put dates or categories in the first column and each series in its own column.
Formula: observation ÷ base-period value × 100
Ready: 2 series across 5 shared periods. Every series will equal 100 at 2020.
Processed in your browser. Your pasted data is not uploaded by this tool.
Live result
Relative performance, made comparable.
Keep the normalized data and continue with themes, annotations, source notes, and export formats.
Continue in Charted →Index number formula
One baseline. Comparable movement.
For each series, divide every observation by that same series’ value in the selected base period, then multiply by 100.
Formula
(observation ÷ base value) × 100
An index of 130 means the series is 30% above its base-period level. It does not mean 130% growth, and it no longer carries the original unit.
| Year | Raw value | Calculation | Index |
|---|---|---|---|
| 2022 | 80 | (80 ÷ 80) × 100 | 100.0 |
| 2023 | 92 | (92 ÷ 80) × 100 | 115.0 |
| 2024 | 88 | (88 ÷ 80) × 100 | 110.0 |
| 2025 | 104 | (104 ÷ 80) × 100 | 130.0 |
When to use it
Use indexing for relative performance.
- Compare assets with different prices from the same market date.
- Compare newsletter subscribers, site visits, and downloads since launch.
- Compare wages, prices, output, or traffic series that begin at different levels.
- Show which region, product, or cohort grew faster from a shared event.
When not to use it
Keep raw values when scale is the story.
- Total budgets, populations, emissions, revenue, or capacity must remain comparable in absolute terms.
- The series use incompatible definitions, frequencies, seasonal adjustments, or coverage.
- The proposed base value is zero, missing, near zero, or chosen to create a preferred winner.
- Readers need to know both relative growth and material size; publish an absolute view alongside it.
Need to explain the method to readers?
The full guide covers base-period selection, date alignment, index-point interpretation, nominal vs. real values, common errors, and copy-ready methodology language.
Questions behind the calculation.
What does index to 100 mean?
Each series is divided by its value in a selected base period and multiplied by 100. The base becomes 100, so an index of 135 means the series is 35% above its base-period value.
What is the formula for indexing data to 100?
For every series, calculate (observation ÷ that series’ base-period value) × 100. Each series uses its own base value at the same shared period.
Can I compare series with different units?
Yes, when the question is relative change. Indexing removes the original unit and starting scale, so prices, rates, counts, or other compatible measures can be compared by their movement from a common date.
How do I choose a base period?
Choose a meaningful period shared by every series, such as the start of a year, policy, campaign, or market event. Avoid missing values, zero, values near zero, or a cherry-picked high or low.
Can I use a base value of zero?
No. Division by zero is undefined, so the series cannot be indexed from that period. Select another valid base period or use a different analytical approach.
Does indexing change the growth rate?
Indexing rescales a simple series and preserves its relative changes and shape. It removes absolute scale, however, and the selected base can change how gaps between multiple series appear.
When should I not index data?
Use raw values when absolute size is the point—for example, comparing budgets, populations, revenue, emissions, or capacity. An indexed chart answers relative performance, not total magnitude.
Is my pasted data uploaded?
No. This calculator parses and transforms the pasted data in your browser. You can download the indexed CSV or carry it into the Charted editor.