for laboratory assays

Curve fitting


Curve fitting Windows Mac Linux

Microsoft ExcelLibreofficePython and RIn web browser

Curve Fitting for Assays – Excel add-in and API


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Plate layout to identify calibrator position and concentration


Example templates


Select calibrator data from layout


Output curve fit graph with data points, fitted curve and unknown values

Excel add-in for curve fitting

Assayfit Pro is an Excel add-in and API service for Mac Os and Windows. Curve fitting can be performed directly from measured data in Excel or from virtually any other application.

Download Add-in

Libreoffice and Openoffice templates

Assayfit pro also supports curve fitting from Libreoffice and openoffice.
Templates are available in the example section

Improved online template

Assayfit pro can be used directly from a web page.
Try our latest online template here by clicking on this button

Any software and cross platform

Any software and cross platform

Assayfit Pro curve fitting for laboratory assays and other scientific data provides maximum flexibility as it can be used on any operating system and from many existing software packages.Use curve fitting functions like four parameter logistic, five parameter logistic and linear and Passing Bablok regression in Excel, Libreoffice, Python, R and online.Create calibration curves and calculate unknown values.

Download Add-in

Use it to automate curve fitting and write your own scripts. A free API key is available. Paid plans provide additional features. Join now and try examples in Excel, R, Python and others.



Fit functions

  • Linear curve fitting
  • Linear Passing-Bablok regression
  • Linear Deming regression
  • 4PL Four parameter logistic
  • 5PL Five parameter logistic
  • second order polynomial
  • third order polynomial
  • Point to point (cubic spline)
  • Univariate spline
  • your own fit function (inquire)

Fit input parameters

  • x and y data
  • Weights
  • Custom start values
  • Apply fit limits
  • fit function
  • Extrapolate
  • Calculate unknown y value from calibration curve
  • Calculate unknown x value from calibration curve
  • 96 well input
  • Plate layout
  • Sample ID

Output parameters

  • xdata (your standard x values)
  • ydata (your standard y values)
  • residuals
  • weights
  • parameter start values
  • parameters after optimisation
  • SD or upper an lower limit of the parameters (for some functions)
  • weighted sum of squares
  • correlation coefficient (for linear fits)
  • Calibration curve limits
  • yknown values (values of which you known the y value and want to calculate the fitted x value)
  • x values calculated from y values
  • xknown values (values of which you know the x value and want to calculate the fitted y value
  • y calculated from xknown values
  • x coordinates of the fit curve (100)
  • y coordinates of the fit curve (100)


  • Javascript curve fitting
  • Standard curve Excel
  • Dose response curve excel
  • Polynomial regression Excel
  • Excel automation example
  • Nonlinear regression in r
  • Curve fit python
  • C# curve fitting
  • template
  • (linear) regression java
  • Any other sofware which can send http get and post commands

Cross platform use

  • Excel Add-in for Mac OS and Windows
  • Libreoffice – Openoffice templates fro Mac Os, Windows and Linux.
  • Software API to create your own software
  • Online curve fitting tool


  • Support over email and phone (only if required)
  • Help with creating templates or software (inquire)
  • Free trial of full service


  • Free no registration
  • 0
  • 15 curve fits per day
  • 20 standards
  • 100 unknowns
  • No registration required
  • Free templates and add-in
  • API key “free”
  • Get started

  • Free plan
  • 0
    2 weeks
  • 50 curve fits
  • 500 standards
  • 500 unknowns
  • Registration required
  • Free templates and add-in
  • Individual API key
  • Join

  • Individual plan
  • 9.99
    1 month
  • Unlimited curve fits
  • 500 standards
  • 500 unknowns
  • Inidividual account
  • Free templates and add-in
  • Individual API key
  • Buy

  • Group plan
  • 39.99
    1 month
  • Unlimited curve fits
  • 500 standards
  • 500 unknowns
  • Share with your team
  • Free templates and add-in
  • Group API key
  • Buy

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