There are a couple banner advertisements in the corner each time you open a new tab. We get paid for these advertisements, and are able to give the profits to charities that partner with us. Tab for a Cause is free to use and always will be.
No matter what our costs are, we give at least 30% of our revenue to charity. At times we’ve given upwards of 90%. We use the rest of the revenue for two purposes: (1) to cover costs, which include hosting/server costs and internal company expenses; and (2) to reinvest in getting more Tabbers so that we can give more to charity in the long term.