how do you make a prediction in excel. What is the formula?

[Barrys]

looking at data from past days and weeks. Need to make a prediction for next week etc

[JohnD]

If the past data can be adequately described by a straight line, you can do it directly in Microsoft Excel using the FORECAST function. For more general behaviour (e.g. polynomial, power function, exponential), you'll need to use one of the built-in regression tools - try putting "curve fit" or "regression" in to the help tool. For really sophisticated modelling, you'll need to roll your own models in Solver.

[JohnD]

If the past data can be adequately described by a straight line, you can do it directly in Microsoft Excel using the FORECAST function. For more general behaviour (e.g. polynomial, power function, exponential), you'll need to use one of the built-in regression tools - try putting "curve fit" or "regression" in to the help tool. For really sophisticated modelling, you'll need to roll your own models in Solver.