Since I moved to the USA, I had some interesting conversations with my friends around what is the custom of tithing here. The answers were always mixed. Some would say you should give 10% of gross income, others say it is 10% of net income, yet others would say 5% to the church and 5% to the charity institutions.
In my home country, what I generally heard from priests (although there were some variations) is that you should give 10% of your disposable income, but I never heard this here.
The USCCB offer no guidelines here. Neither does my diocese. However, I did find varying opinions from other dioceses and sites.
The archdiocese of Saint Louis , Charleston Diocese, Rockford Diocese have guidelines saying we should give 5% to the Church and 5% to charities using the gross income as basis for our calculations. The diocese of Wichita suggests 8% to the Church and 2% to charities. The diocese of Dodge City says "(t)oday, the Church does not ask us to tithe", but suggests 10%.
In an article of Catholic.com it cites the Canon Law and the Catechism of the Catholic Church and shows there is no percentage fixed for tithing. The Diocese of Burlington goes in the same direction "No percentage has been prescribed universally for supporting the work of our New Testament priests in the Catholic Church. But the Old Testament 10-percent precedent is worth considering. As a 'law,' even 1 percent of a Catholic’s income would suffice as a minimum for the precept “provide for the needs of the Church” (Catechism of the Catholic Church#2043)".
Which lead me to the Catechism of the Catholic Church 2043 that says:
"The fifth precept ("You shall help to provide for the needs of the Church") means that the faithful are obliged to assist with the material needs of the Church, each according to his own ability."
I discussed this with my go to priest here in USA (you should do the same) and he adheres to the Catechism above. You must assist with the material needs of the church but according to your own ability.
So, be generous, despite the impressions a capitalist and materialist world cause in us, we usually have more than we need and we can help more than we think...