# Tag Info

The risk-neutral probability measure is defined in terms of its numeraire. For the usual risk-neutral probability measure the numeraire is the bank account, $\beta(t)$. If we have a tradeable asset $X(t)$ then $\tilde{X}(t)=\frac{X(t)}{\beta(t)}$ is a martingale under $\mathbb{Q}$ meaning that $$\tilde{X}(t)=\mathbb{E}_{t}^{\mathbb{Q}}(\tilde{X}(T))$$ So we ...