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Reinvest each maturity payment in the next unit-principal zero-coupon bond. Positive bond prices make the resulting self-financing portfolio strictly positive, so it can be used as a numéraire. Its one-step growth is the reciprocal of the current one-period bond price.

For a maturity $T$, the T-forward measure uses the zero-coupon bond maturing at $T$ as numéraire. If $B_t^T$ is its time-$t$ price, an attainable payoff $X_T$ has value $B_t^T{\mathbb{E}}_{Q^T}[X_T\mid {\mathcal{F}}_t]$.