  We show how to simplify the calculation of the finite contributions from
heavy particles to EFT Wilson coefficients by using on-shell methods. We apply
the technique to the one-loop calculation of $g-2$ and $H\gamma\gamma$, showing
how finite contributions can be obtained from the product of tree-level
amplitudes. In certain cases, due to a parity symmetry of these amplitudes, the
total contribution adds up to zero, as previously found in the literature. Our
method allows to search for new natural zeros, as well as to obtain non-zero
contributions in a straightforward way.
