A well-known formula of R J Herbert’s relates the various homology classes
represented by the self-intersection immersions of a self-transverse immersion. We
prove a geometrical version of Herbert’s formula by considering the self-intersection
immersions of a self-transverse immersion up to bordism. This clarifies the geometry
lying behind Herbert’s formula and leads to a homotopy commutative diagram of
Thom complexes. It enables us to generalise the formula to other homology
theories. The proof is based on Herbert’s but uses the relationship between
self-intersections and stable Hopf invariants and the fact that bordism of
immersions gives a functor on the category of smooth manifolds and proper
immersions.