I plotted months vs numbers in excel and got a trend line with an equation.
When I try to put my xaxis (months) in the trend equation I am getting
strange results. -ve results why so? If I replace months with numbers then I
get the right answere.

Secondly, my graph appears to fit best with the moving average trend but I
cann't see the R2 value and the equation for future predictions.

What is the easiest way to predict future using trend lines or other
features of Excel