Cross the €603 Minijob ceiling by even a single euro and, historically, employees faced a sudden jump straight to full-rate social insurance contributions. The Übergangsbereich exists to smooth that cliff: instead of an all-or-nothing switch, your own contribution phases in gradually across the band, growing from close to zero right above the Minijob floor to the full standard-employee rate exactly at the €2,000 ceiling.
The mechanic behind that smooth phase-in is Faktor F, a legally defined constant recalculated each year from the average combined employer-and-employee social insurance rate. It feeds into a formula that produces a reduced assessment income, lower than your actual gross pay, which the standard contribution rate is then applied to. The result is a contribution that rises with your real income but always lands below what a standard employee at the same gross would pay, until the two converge exactly at the ceiling.
Only your side of the equation is reduced. Your employer's contribution is always calculated on your actual, full gross pay at the normal employer rate, with no discount whatsoever. The Gleitzone exists purely to protect the employee from a sudden cost jump, not to lower what it costs a business to employ someone in this band.
Income tax sits outside all of this. Midijob pay is ordinary Lohnsteuer income, taxed via the same progressive §32a formula as any other salary, so the savings you see here are specifically a social insurance effect, not a tax break.
