We investigate sufficient conditions for the invariance of the real Milnor number under \( \mathcal {R} \) -bi-Lipschitz equivalence for function germs \( f, g :(\mathbb {R}^n, 0) \rightarrow (\mathbb {R}, 0) \) . More generally, we explore its invariance within the extended framework of \( \mathcal {R} \) -asymptotically Lipschitz equivalence. To this end, we introduce the \(\alpha \) -derivative of maps, which provides a natural setting for studying asymptotic growth. Additionally, we discuss the implications of our results in the context of \( C^k \) and \( C^{\infty } \) -equivalences, establishing sufficient conditions for the real Milnor number to remain invariant.