A volatile formula is a formula in a spreadsheet application, such as Microsoft Excel, that contains one or more volatile functions. These functions are unique because their results can change every time the spreadsheet performs a calculation, even if none of the arguments or precedent cells for that function have changed. Essentially, a volatile function's value is recalculated each time the cell is calculated, and this recalculation occurs every time Excel (or the spreadsheet program) recalculates.
Understanding Volatile Functions
Volatile functions are distinct from non-volatile functions. While most functions only recalculate when their input values or arguments change, volatile functions do not depend on such changes. They are designed to update their output whenever the entire spreadsheet or a specific part of it is recalculated.
Here's how they work:
- Triggered Recalculation: Volatile functions recalculate whenever a calculation event occurs in the workbook. These events can include:
- Opening the workbook.
- Making any change to any cell in the workbook.
- Adding, deleting, or renaming a worksheet.
- Inserting or deleting rows/columns.
- Manually forcing a recalculation (e.g., by pressing F9).
- Saving the workbook.
- Independent of Arguments: Unlike typical functions, their value can change even if none of the function's arguments change. This is the core characteristic that defines them as volatile.
Common Volatile Functions in Spreadsheets
Several built-in functions are known to be volatile. Understanding which functions fall into this category is crucial for efficient spreadsheet design.
NOW(): Returns the current date and time. This value constantly updates with every recalculation.- Example:
=NOW()
- Example:
TODAY(): Returns the current date. LikeNOW(), it updates whenever the sheet recalculates.- Example:
=TODAY()
- Example:
RAND(): Generates a random number between 0 and 1.- Example:
=RAND()
- Example:
RANDBETWEEN(): Generates a random integer between two specified numbers.- Example:
=RANDBETWEEN(1,100)
- Example:
OFFSET(): Returns a reference to a range that is a specified number of rows and columns from a cell or range of cells. This function is often considered volatile, especially if its arguments are not static.- Example:
=SUM(OFFSET(A1,1,1,1,1))
- Example:
INDIRECT(): Returns the reference specified by a text string. Since the text string could potentially refer to different cells dynamically, this function is volatile.- Example:
=SUM(INDIRECT("A"&B1))
- Example:
CELL(): Returns information about the formatting, location, or contents of a cell. Its volatility depends on theinfo_typeargument, but it often triggers recalculations.- Example:
=CELL("address",A1)
- Example:
INFO(): Returns information about the current operating environment.- Example:
=INFO("osversion")
- Example:
Note: User-Defined Functions (UDFs) written in VBA can also be explicitly declared as volatile using Application.Volatile.
Impact on Performance
The frequent recalculation of volatile formulas can significantly affect spreadsheet performance, especially in large and complex workbooks.
- Cascading Recalculations: When a volatile function recalculates, it forces all formulas that depend on its result (its "dependents") to also recalculate. This can create a chain reaction, leading to a substantial portion, or even the entirety, of the worksheet or workbook being recalculated unnecessarily.
- Slow Response Times: In workbooks with many volatile formulas, users may experience noticeable delays and slower response times when performing actions like entering data, applying filters, or opening the file. This is because the calculation engine is constantly busy re-evaluating these functions.
Best Practices for Using Volatile Formulas
While volatile formulas have their uses, it's wise to manage their application carefully to maintain optimal spreadsheet performance.
- Use Sparingly: Employ volatile functions only when absolutely necessary. If a static value or a non-volatile alternative can achieve the same result, prioritize that option.
- Minimize Scope: If you must use a volatile function, try to limit the number of cells it affects. For example, if you only need the current date in one cell, don't use
TODAY()in hundreds of cells. - Alternative Approaches:
- For dynamic range referencing, consider using
INDEXandMATCHinstead ofOFFSETandINDIRECT, asINDEXandMATCHare generally not volatile. - If you need a timestamp, consider using a VBA macro to insert the current date/time as a static value, rather than a
NOW()formula that constantly updates.
- For dynamic range referencing, consider using
- Manual Calculation Mode: For very large workbooks with extensive volatile formulas, switching the calculation mode to "Manual" can help. This allows you to control when calculations occur (usually by pressing F9), preventing constant recalculations during data entry.
- Helper Cells: If a volatile function's output is needed multiple times but doesn't need to update with every single recalculation, you can place the volatile function in a single helper cell and then reference that helper cell elsewhere. This centralizes the volatility.
Volatile vs. Non-Volatile Functions
Here's a quick comparison to highlight the key differences:
| Feature | Volatile Formula | Non-Volatile Formula |
|---|---|---|
| Recalculation | Every time the workbook or sheet recalculates | Only when its arguments or precedents change |
| Value Change | Can change even if arguments are unchanged | Changes only if arguments or precedents change |
| Performance | Can significantly impact performance due to frequent updates | Generally has better performance as it calculates less often |
| Examples | TODAY(), NOW(), RAND(), OFFSET(), INDIRECT() |
SUM(), VLOOKUP(), INDEX(), MATCH(), AVERAGE() |
