# Definition of wilder's moving average

https://www.marketvolume.com/technicalanalysis/wildersvolatility.asp

I see this page describes wilder's moving average. But the first step ATR = SMA(TR) is not clear. How many periods should be used to compute this simple moving average? Should it be N?

...
Step #2: Apply the moving average to the defined TR.

ATR = SMA(TR)

Wilder uses simplified formula to calculate Average of True Range:

ATR = Wilder's Volatility = ((N-1) x Previous ATR + TR) / N
...
$$`$$

### Yes, the SMA should be computed with $$N$$ periods in your situation:
In conclusion, he recommends the average true range (ATR) to be computed with a period of 14 days (ie. a 14-day SMA) which is equivalent to $$N$$ in your situation.
$$VI_{today} = \frac{13 \cdot VI_{previous} + TR_1}{14},$$ where $$TR_1$$ is today's true range. This is equivalent to $$N=14$$ in your specified formula.