How do I interpolate numbers in Excel?

[Guest]

I was trying to interpolate numbers by using Forecast, but it is not the
linear interpolation result I need. I am wondering is there a way to do it?

Following is Forecast help example. By using Forecast, the result is 10.6,
but if using interpolation, Known Y (7,9) Known X (28,31), the result should
be 8.333

Known Y KnownX
6 20
7 28
9 31
15 38
21 40
Formula Description (Result)
=FORECAST(30,A2:A6,B2:B6) Predicts a value for y given an x value of 30
(10.60725)

Thank you very much in advance !!!!!!

 

[Niek Otten]

I think you are confusing Y and X

 

[Mike Middleton]

The example fits a straight line using all five values and bases the
forecast on that fitted line.

For interpolation between two points, use only the two adjacent values for
the straight-line forecast:

=FORECAST(30,A3:A4,B3:B4)

or

=FORECAST(30,{7,9},{28,31})

and the result is 8.3333.

- Mike
www.mikemiddleton.com

 

[Bruce Sinclair]

I was trying to interpolate numbers by using Forecast, but it is not the
linear interpolation result I need. I am wondering is there a way to do it?

Following is Forecast help example. By using Forecast, the result is 10.6,
but if using interpolation, Known Y (7,9) Known X (28,31), the result should
be 8.333

Known Y KnownX
6 20
7 28
9 31
15 38
21 40
Formula Description (Result)
=FORECAST(30,A2:A6,B2:B6) Predicts a value for y given an x value of 30
(10.60725)

Thank you very much in advance !!!!!!

You could use the slope and intercept functions and calculate the numbers
you ned using those. That way the function doesn't get in the way of what
you are trying to do


Bruce

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[gjcase]

You can plot the data & insert a non-linear trendline, using the option
to display the quation on the chart, then use that equation to back out
your intermediate values.

---GJC