Why Excel Logarithmic Trendline R² Differs from LINEST and How to Check It
Question details
The user needs to understand why the R² displayed on an Excel logarithmic trendline can differ from an R² calculated after transforming x with LOG10 and using linear regression or LINEST.
- Product
- Microsoft Excel and WPS Office Spreadsheets
- Device & OS
- not provided
- Scenario
- The user created a logarithmic trendline in Excel and compared its displayed R² with an R² from LOG10-transformed x values and linear regression/LINEST.
- Observed behavior
- The R² values differ, so the user wants to know which calculation is correct for a logarithmic model and how to verify it.
Before comparing the values, note the exact trendline equation shown on the chart and confirm whether the selected chart data range matches the LINEST or RSQ input range.
Check the Logarithmic Trendline Equation, Data Range, and Intercept Setting
Use this first to verify whether the chart trendline and the LINEST formula are based on the same selected data and model options.
A logarithmic trendline in Excel fits y = a + b*LN(x). If the selected data range, intercept option, or displayed equation differs from the LINEST input, the R² values will not be directly comparable.
Click the chart series, go to Chart Design > Add Chart Element > Trendline > More Trendline Options, and enable Display Equation on chart and Display R-squared value on chart.
In Format Trendline, review the trendline data range and then select the same cells used by the LINEST or RSQ formula.
In Format Trendline, see whether Set Intercept is enabled or the intercept is forced to zero, and match that setting when evaluating the LINEST result.
Use the Correct LOG10 or LN Linearization for a Logarithmic Model
Use this when you want to reproduce the logarithmic fit with LINEST or RSQ from transformed x values.
Check Excel Version and R² Calculation Method for LINEST, RSQ, and Trendline
Use this to confirm whether an Excel calculation difference, such as forced zero-intercept behavior, explains the gap.
Use WPS Office Spreadsheets as a Free Alternative for Logarithmic Trendline and LINEST Analysis
For calculation behavior that is built into Microsoft Excel, WPS Office Spreadsheets provides a free, lightweight alternative with native .xlsx support, a familiar spreadsheet interface, and seamless file migration for reviewing logarithmic trendline and LINEST models.
Frequently Asked Questions
Should I use LOG10 or LN when checking Excel's logarithmic trendline R²?
For Excel's logarithmic trendline y = a + b*LN(x), use LN(x). LOG10(x) can also linearize the model if the base is accounted for; do not transform y unless your intended model requires it.
Why does LINEST R² change when I force the intercept to zero?
Forced zero-intercept changes the coefficient of determination definition and removes the intercept from the fitted model, so LINEST R² and the chart trendline R² can differ significantly.
How can I compare Excel trendline R² with RSQ?
Display the trendline equation, calculate fitted y values for each original x, and use =RSQ(original_y, fitted_y). Compare that to the chart's displayed R².
Does WPS Office Spreadsheets support logarithmic trendlines and LINEST?
Yes, WPS Office Spreadsheets supports chart trendlines and compatible LINEST/RSQ formulas in .xlsx workbooks, so you can review the same model without changing the file format.
