The demo file contains Cardinal Spline & Cubic Spline & Monotone Cubic Spline UDF (User Defined Functions) that create curves that go exactly through all your data points. The advantage of a monotone cubic spline is that it does not 'wobble' at local minima and maxima.

Download demo file
(135kB - downloaded 2501 times - Latest version: 2022-01-11, now including both regular function that returns a single Y value, given X and the datapoints, and array function that creates a table with X and Y values, given the number of segments to be created between the datapoints provided.)

If you want to interpolate both X and Y values within a 2-dimensional table, then see Bilinear interpolation (linear plus spline based).

MS Excel VBA code to be put in a module - array functions

In MS Excel, press Alt+F11 to open the Visual Basic Editor (Windows). Via top menu: Insert → Module. Copy the MS Excel VBA code of the functions into the module.

Your input data can now be column organized (default table) or row organized (transposed default table).

Regular function - Single Y value output only, given X value

In MS Excel, press Alt+F11 to open the Visual Basic Editor (Windows). Via top menu: Insert → Module. Copy the MS Excel VBA code of the functions into the module.