File Exchange > Graphing >    Simple Fit

OriginLab Technical Support
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Simple Fit.opx
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A simplified tool to perform curve fitting.

Screen Shot and Video:

  1. This tool provides a convenient way to perform curve fitting. With the data plotted, simply open the tool, type the desired equation, specify initial parameters and generate your report. You do not need to even save or create a fitting function.

The tool only supports one independent variable (x) and one dependent variable (y).

Download the file Simple Fit.opx, and then drag-and-drop onto the Origin workspace. An icon will appear in the Apps Gallery window.


  1. Create a graph of the XY data with optional error bars, and click the Simple Fit app icon.
  2. If error bar is present in the graph, you can optionally perform a weighted fitting by checking the Weighted Fit check box..
  3. Define the fitting function:
    • To use an existing function, check the Use Existing Function check box and select desired function.
    • To use a new function, uncheck the Use Existing Function, enter the function definition into the "y(x)" edit box, using "x" as independent variable.
  4. Specify or change desired initial parameter values.
  5. Click the 1 Iter. button to perform one iteration at a time, or the Fit button to perform iterations until the tolerance is reached or the number of iterations has reached 400 or an error occurs. Before each operation, you can change the parameter values or fix status.
  6. To save the fitting function, click the Save as... button. The fitting function will be saved in User Defined category.
    If you do not save the function, it will not be available for selection next time the tool used.

NOTE: When performing weighted fitting, the error values reported for fit parameters are NOT scaled by the sqrt(reduced chi-square) value.

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v 1.1: More accurate syntax checking.

Reviews and Comments:
01/21/2017kapilchaudharigood one

10/23/2015RiverFallsThis app provides a much quicker, one-screen interface for doing one variable nonlinear curve fits. This is a much better way to do curve fitting for simple functions, or if you are not a curve fitting expert.
As a bonus, the uncertainties in the fit parameters are reported such that they account for the error bars of the data (which is not the default in the 'regular' curvefitting interface in Origin).