Power BI what-if parameters: let readers test a scenario
Power BI what-if parameters let a reader change an input, such as a discount rate, and watch the report recalculate. The author creates a parameter with a range of values, and a slicer lets the reader pick one. Measures then use the chosen value in their formulas. Microsoft's current menus call the feature a numeric range parameter. This guide covers setup, a worked example and the limits.
- Slicer-driven scenarios
- Setup in four steps
- Two documented limits
Last updated
What are Power BI what-if parameters?
A normal report shows what happened. A what-if report also shows what would happen under a different assumption. For example, how do sales look after a discount of a chosen size?
Power BI Desktop handles this with a parameter. Microsoft describes it as a way to store a variable that readers can adjust with a slicer. When you create one, Desktop also creates a measure that returns the currently selected value.
Both objects become part of the model. Therefore they work on every page of the report, not only on the page where you made them. You can even delete the slicer and add it back later from the field list.
Create Power BI what-if parameters in four steps
The path below follows Microsoft's article for Power BI Desktop, using the numeric range type.
Open New parameter
First go to the Modeling tab and select New parameter. Then choose Numeric range as the type.
Define the range
Next enter a name, a data type, a minimum, a maximum and an increment. The increment sets how far each slicer step moves.
Add the slicer
Then keep the option that adds a slicer to the page, and select Create. The slicer appears on the current page.
Write the scenario measure
Finally create a measure that uses the parameter's value measure in its formula, and place it in a visual.
How does a parameter change a measure?
The parameter alone changes nothing. A measure has to read it. Microsoft's example stores a discount rate, then writes a measure for sales after discount. The formula takes total sales and subtracts total sales multiplied by the selected rate.
After that, the author builds a column chart with the order date on the axis. It shows the original sales amount beside the discounted one. When a reader moves the slider, the discounted columns change at once, while the original ones stay put.
So the pattern has three parts: a parameter, a slicer and at least one measure that refers to the parameter. If a scenario seems to do nothing, check first whether any measure actually uses the value.
Three scenarios that suit a slider input
Microsoft mentions discounts and sales goals, and the same pattern extends to other planning questions.
Discount impact
A sales lead sets a discount rate and sees revenue after the reduction. As a result, a pricing talk starts from shared figures.
Goal-based pay
Salespeople move a target slider and see how their compensation would change when they meet a given goal.
Growth assumptions
A planner adjusts an expected growth rate, and a projection measure then recalculates next year's figure from this year's base.
Which limits apply to Power BI what-if parameters?
Microsoft documents two limits. First, a parameter can have at most 1,000 unique values. If the range and increment produce more, Power BI samples the values evenly. So a very fine increment over a wide range will skip some steps.
Second, parameters are designed for measures within visuals. When you use one in a dimension calculation, the value might calculate incorrectly. Therefore keep the logic in measures, and do not feed the value into a column that groups data.
There is also a small entry rule. For decimal numbers, type a leading zero before the decimal point. Otherwise Power BI cannot validate the value, and the Create button stays unavailable.
Good practice for scenario slicers on a report page
A scenario only helps when readers understand what they are changing, so design the page around that.
- Label the slicer with the business term, not a field name
- Show the selected value on a card beside the chart
- Place actual and scenario figures side by side
- Choose an increment that matches real decisions
- State the assumption in a short note on the page
- Keep scenario pages apart from official results
Power BI what-if parameters: frequent questions
Where did the What if button go in Power BI Desktop?
Microsoft's current article describes the route as the Modeling tab, then New parameter, then Numeric range. The same dialog also offers a Fields type, which lets readers switch the fields a visual shows. So the what-if idea lives on under the numeric range option. Check your version's ribbon, since menus change between releases.
Can I use a what-if parameter on more than one page?
Yes. After you create it, the parameter and its measure belong to the model. Microsoft notes that they are available throughout the report. To add the slicer on another page, drag the parameter from the field list onto the canvas and change the visual to a slicer.
Why does my slider skip values?
Because of the documented cap on unique values. When a parameter would hold more than 1,000 of them, Power BI samples the values evenly. As a result, some steps disappear. Widen the increment or narrow the range, and the slider will then stop on every value you defined.
Does a what-if parameter in Power BI change the source data?
No. The parameter is a small table of values inside the model, and the slicer only selects one of them. Measures read that selection and recalculate. Nothing writes back to the source system. So readers can explore freely, and the underlying data stays exactly as it was.
Can Power BI Agency build a scenario model for our team?
Yes. One of our consultants agrees the assumptions that matter with your team, then builds the parameters and measures behind them. We work online in your own Microsoft tenant and fix the scope in a written quote. Power BI Agency is a division of Sataware Technologies and independent of Microsoft.
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