Interstitial atoms can cause dechanneling either in one large angle single scattering event (instantaneous dechanneling) or can induce dechanneling by a small angle deflection after which the projectile loses its alignment in successive interactions with lattice atoms and crystal electrons (delayed dechanneling). For 2 MeV He+ions passing along ⟨100⟩ in a silicon crystal it is calculated that delayed dechanneling is 1.7 and 2.5 times more effective than instantaneous de-channeling by interstitial gallium positioned at the channel center or at the hexagonal and ytterbium sites, respectively. The results demonstrate that flux peaking, transverse energy distribution of the projectiles, and interstitial position play an important role in any dechanneling process.