INTERPOLATE - Interpolation and Extrapolation

Estimate the value of the function represented by (x,y) data set at an intermediate x-value.


INTERPOLATE(X, Y, target, Method, extrapolate)

is the x-component of the input data table (a one-dimensional array of cells (e.g., rows or columns)).
is the y-component (i.e., function) of the input data table (a one-dimensional array of cells (e.g., rows or columns)).
is the desired x-value(s) to interpolate for (a single value or a one-dimensional array of cells (e.g., rows or columns)).
is the interpolation method (1 = Forward Flat, 2 = Backward Flat, 3 = Linear, 4 = Cubic Spline).
Value Method
1 Forward Flat.
2 Backward Flat.
3 Linear (default).
4 Cubic Spline.
sets whether or not to allow extrapolation (1 = Yes, 0 = No). If missing, the default is to not allow extrapolation.
Value Extrapolate
0 No (default).
1 Yes.


INTERPOLATE(.) function is deprecated as of version 1.68.4: use NxINTRPL(.) function instead.


  1. The X and Y array sizes must be identical.
  2. The X-array and Y-array both consist of numerical values. Dates in Excel are internally represented by numbers.
  3. The values in the X-array can be unsorted and may have duplicate values.
  4. In the case where X has duplicate values, INTERPOLATE will replace those duplicate values with a single entry, setting the corresponding y-value equal to the average.
  5. The X and/or Y arrays may have missing values (#N/A). In this case, INTERPOLATE will remove those entries.
  6. For cubic spline interpolation, we construct a set of natural cubic splines that are twice continuously differentiable functions to yield the least oscillation about the function f which is interpolated.

Files Examples

Related Links


  • Kincaid, David; Ward Cheney (2002). Numerical Analysis (3rd edition). Brooks/Cole. ISBN 0-534-38905-8. Chapter 6.
  • Ahlberg, Nielson, and Walsh, The Theory of Splines and Their Applications, 1967.


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