Formula to find trend line value from slope value...

[richardcarter]

Ive seen many posts relating to equations and formulas to find trend line values from a set of data using LINEST, EXP and LN, but I haven't been able to find anything that will help me find a trend line value where the slope value is already known - so hoping someone can help.

In a nutshell, I have a straight trend line on a semi-log chart (y values are log, x values are linear). The y axis represents quantity and the x axis represents time (number of days). The trend line starts at a y value of 12, and an x value of 1 (i.e. day 1). The slope of the trend line is -0.05308. My question is: What formula would calculate the value of the trend line as at day 12?

Many thanks.

 

[ChrisM]

Every day the value changes by the slope, so to find the 12th day it's just

=StartValue + (Slope * DayNumber)

=12 + (-.05308 * 12)

 

[richardcarter]

Many thanks for that... I now understand that the slope value I have has already accounted for the fact that it is a log trendline.. I was on the understanding that it hadn't, and was therefore scratching my head as to how to convert it to log basis - but you've cleared it up for me.. thanks again!

Every day the value changes by the slope, so to find the 12th day it's just

=StartValue + (Slope * DayNumber)

=12 + (-.05308 * 12)