What is a purification rate?

The proportion of a distribution that came from impermissible income and should be given away rather than kept.

A screened company can still earn a small amount of interest or other non-permissible income. The fund's Shariah adviser calculates what proportion of income that represents and publishes it as a rate - for example 0.42% of distributions for the year.

You apply the rate to what you received and donate that amount, with no expectation of reward and no tax benefit claimed. Purification is separate from zakat and does not replace it.