How do I determine if a compound is cell-permeable?

How do I determine if a compound is cell-permeable？

There is no easy way of predicting if a product will be cell-permeable. Generally charged molecules are not cell-permeable. However, modified phosphorylated compounds, such as mono- and dibutyryl cAMP, are cell-permeable. High molecular weight peptides are generally not cell-permeable under normal conditions.