We report spontaneous translocation of a single cell-penetrating peptide (CPP) across a model membrane using the weighted ensemble (WE) method within the molecular dynamics (MD) simulations approach. Furthermore, we show that a water pore plays a crucial role in translocating the peptide and a tilt angle of the peptide also affects the translocation. Last, using umbrella sampling, we obtain the potential of mean force (PMF) along the translocation path and show that a single CPP’s translocation is energetically unfavorable.