There are various options for calculating the trendline.  Select the appropriate option.

Trendline typeDescription
ExponentialAn exponential trendline is a curved line that is most useful when data values rise or fall at increasingly higher rates.
LinearA linear trendline is a straight line that best fits the data using the least squares method. It is used to show a steady rate of increase or decrease.
LogarithmicA logarithmic trendline is a best-fit curved line that is most effective when the rate of change in the data increases or decreases quickly and then levels out.
PolynomialA polynomial trendline is a curved line that is used when data fluctuates, particularly for analysis of variables that vary by quadratic or cubic orders.
PowerA power trendline is a curved line that is ideal for datasets that compare measurements that rise at a specific rate, useful when data is proportional to its power.
Moving AverageA moving average trendline smooths out fluctuations in data to show a pattern or trend by averaging the data points in a specific interval.