In this paper the locations where ρ~app~ = ρ~1~ and ϕ = π/4 and where these parameters reach an extreme value in two‐layer magnetotelluric (MT) sounding curves are summarized in an extremely compact form. The key parameters over two‐layer models with conductivities σ~1~, σ~2~ and upper layer thickness h are the real S and α, where S is the conductivity contrast and α is the distance between the observation site and the conductivity interface, normalized to the half skindepth in the first layer. If the impedance components, various resistivity definitions ( ρ~Re Z~, ρ~Im Z~ and ρ~|Z|~, based on different parts of the complex impedance Z ) and the magnetotelluric phase ϕ are derived as a function of S and α, then the conditions for the apparent resistivity ρ~app~ and the phase ϕ are that they either satisfy ρ~app~ = ρ~1~ and ϕ = π/4 or attain extreme values which can be given in terms of simple algebraic equations between S and α. All equations are valid for observation sites at any depth 0 ≤ z ≤ h in the first layer. The set of equations, presented in a tabular form, may make it possible to determine a layer boundary from the short period part of the sounding curves, in particular the ρ~Re Z~ and the ϕ~MT~ curves.