Due to the nature and sanctity of this commitment, there is no prescribed way to calculate the 7%. However, here are some general guidelines:
It can be based either on gross or net income, pre or post tax; revenue or profits.
If you have a business and salaried income (or other sources of income), you can include all your income in calculating 7% contributions. For example, you can make a yearly contribution for your business income and periodic contributions for your salary income.
If you and your spouse are both earning and willing to contribute, you can either register for Ishanga 7% as two separate contributors (hence, two separate IDs) or include the joint income in calculating the 7%. This may also depend on how you prefer to file taxes, jointly or separately. Alternatively, if your partner is not yet ready to join the program, you can make the contributions based on your income alone.