# Trend lines and forecasting models

*Tableau Data Analyst Study Guide · Explore and Analyze Data · Last updated October 29, 2026 · https://www.certifyforce.com/study-guide/tableau-data-analyst/explore-and-analyze-data/trend-lines-and-forecasting-models*

Add and edit trend lines (model types, factors, per-color lines, stacked-bar limits) and judge them with R-squared and p-values, then add a forecast with default settings, clear the view's forecasting constraints and customize length, source data, model and prediction intervals in Forecast Options.

- Certification: Salesforce Tableau Data Analyst
- Exam section: Explore and Analyze Data
- Study guide: https://www.certifyforce.com/study-guide/tableau-data-analyst

**Official exam objective:**

> Summarize, model, and customize data by using the Analytics pane: Totals and subtotals; Reference lines; Reference bands; Average lines; Trend lines; Distribution bands; Forecast by using default settings; Customize a data forecasting model.

## What the exam expects

- Add a trend line from the Analytics pane, pick its model type, and fix a view where trend lines do not appear.
- Edit trend lines: remove a field as a factor, turn off one line per color, force the y-intercept to zero, show confidence bands.
- Judge a trend line with R-squared and p-values from the tooltip and Describe Trend Model.
- Add a forecast with default settings, and remove whatever blocks it (table calculations, totals, disaggregated measures, exact dates).
- Customize a forecast in Forecast Options: length, Aggregate by, Ignore last, model (Automatic or Custom additive/multiplicative) and prediction interval.
- Totals, reference lines, bands, average lines and distribution bands: see Totals, reference lines, bands and distributions.

Key terms:
- **Factor:** a dimension in the view that splits the trend line model into separate lines.
- **p-value:** the probability that the trend equation came from random chance; smaller is more significant.
- **Ignore last:** trailing periods excluded from estimating the forecast model.
- **Prediction interval:** the shaded band the forecast value is expected to fall in at a set percentage.

## Key facts

| Fact | Detail | Source |
|---|---|---|
| Trend line axes | Both must hold a field interpretable as a number | [Add Trend Lines to a Visualization](https://help.tableau.com/current/pro/desktop/en-us/trendlines_add.htm) |
| Stacked bars | No trend lines; clear Analysis > Stack Marks | [Add Trend Lines to a Visualization](https://help.tableau.com/current/pro/desktop/en-us/trendlines_add.htm) |
| Confidence bands | 95% by default; not for Exponential | [Add Trend Lines to a Visualization](https://help.tableau.com/current/pro/desktop/en-us/trendlines_add.htm) |
| Linear R-squared | Equals the square of CORR | [Add Trend Lines to a Visualization](https://help.tableau.com/current/pro/desktop/en-us/trendlines_add.htm) |
| Significant p-value | 0.05 or less is often considered sufficient | [Add Trend Lines to a Visualization](https://help.tableau.com/current/pro/desktop/en-us/trendlines_add.htm) |
| Forecast blockers | Table calcs, disaggregated measures, percent calcs, totals, Exact Date | [Forecasting](https://help.tableau.com/current/pro/desktop/en-us/forecasting.htm) |
| Web editing | Forecast visible, but cannot be added or modified | [Forecasting](https://help.tableau.com/current/pro/desktop/en-us/forecasting.htm) |
| Minimum data | 5 points for trend; 24 for a 12-month season | [How Forecasting Works in Tableau](https://help.tableau.com/current/pro/desktop/en-us/forecast_how_it_works.htm) |
| Finer data | Only for SUM or COUNT measures | [How Forecasting Works in Tableau](https://help.tableau.com/current/pro/desktop/en-us/forecast_how_it_works.htm) |
| Ignore last default | Trims one period | [How Forecasting Works in Tableau](https://help.tableau.com/current/pro/desktop/en-us/forecast_how_it_works.htm) |
| Multiplicative limit | No values less than or equal to zero; no multiplicative trend with additive season | [Configure Forecast Options](https://help.tableau.com/current/pro/desktop/en-us/forecast_options.htm) |
| Band width | Lower percentile gives narrower prediction bands | [Create a Forecast](https://help.tableau.com/current/pro/desktop/en-us/forecast_create.htm) |

## Check yourself

- Why does Tableau not offer confidence bands for an Exponential trend line?
- When is a date part valid for forecasting?
- What does the shaded area on a default forecast show?
- Why does Tableau refuse a multiplicative trend with an additive season?

## Sources

- [Add Trend Lines to a Visualization](https://help.tableau.com/current/pro/desktop/en-us/trendlines_add.htm)
- [Forecasting](https://help.tableau.com/current/pro/desktop/en-us/forecasting.htm)
- [Create a Forecast](https://help.tableau.com/current/pro/desktop/en-us/forecast_create.htm)
- [How Forecasting Works in Tableau](https://help.tableau.com/current/pro/desktop/en-us/forecast_how_it_works.htm)
- [Configure Forecast Options](https://help.tableau.com/current/pro/desktop/en-us/forecast_options.htm)
- [Analytics Pane](https://help.tableau.com/current/pro/desktop/en-us/environ_workspace_analytics_pane.htm)
- [Tableau's Order of Operations](https://help.tableau.com/current/pro/desktop/en-us/order_of_operations.htm)

## About the full unit

The "Core concepts", "Exam traps" and "Worked scenario" sections of this unit, its 10 linked practice questions, and unlimited timed mock exams are included with the Tableau Data Analyst pack (USD $19): https://www.certifyforce.com/practice-exams