AbstractGeneral expressions for electron shakeup and shakeoff probabilities of arbitrary atomic shells under the sudden change in central potential have been obtained in the sudden approximation by the use of non‐relativistic hydrogenic wave functions. The matrix elements for the shakeup and shakeoff processes are expressed analytically in the similar form in terms of the Gauss‐type hypergeometric functions. Many‐electron effect is taken into account through the screened hydrogenic model and the effect of the screening constants is examined. It is found that the shakeup and total shakeoff probabilities can be written in universal form by the use of a single parameter. The dependence of the shake probabilities on this parameter is discussed.