# Skew in Black Scholes model

We are modeling Foreign exchange rates using Black Scholes model given below:

$$F_{t}=F_{t−1} + (r_d−r_f)F_{t−1}dt + \sigma F_{t−1}dW_t$$

Where:

$F_t$ and $F_{t−1}$ are FX rates at time $t$ and $t−1$

$r_d$ domestic short rate

$r_f$ foreign short rate

$dt$ is the change in time period

$\sigma$ is the volatility obtained from ATM volatility surface

$dW_t$ is correlated random number (correlation is between $r_d$, $r_f$, and FX rate)

I ran this model for $1000$ simulations and my percentile graphs show a skew on the positive side of distribution. Can someone please help me understand the skewness.