It amounts to much more than a tithing.
Just take your hourly income/earning rate multiplied by the hours spent for meetings and ministry. See for yourself whether or not it surpasses the 10% mark of your weekly or monthly income; and that figure does not even include gasoline or public transportation charges.
15 What is included in this spiritual tithe? For one thing, we give Jehovah of our time and energy. The time we spend at meetings, in attending assemblies and conventions, in the field service, all of this is something given to Jehovah—a part of our tithe. The time and energy we spend visiting the sick and helping others—again, these are part of our tithe. Assisting in constructing Kingdom Halls and sharing in the work of maintaining and cleaning the hall are likewise a part.
16 Our tithe also includes our financial contributions.
1992 The Watchtower, December 1, page 16, pars. 15-16
In our day the tithe represents the time, energy, and finances that are used directly in Jehovah’s service and in support of the Kingdom work. The tithe includes the time we spend at meetings, assemblies, and conventions, as well as in maintaining and cleaning our meeting places.
Our Kingdom Ministry, May 1993, page 3, par. 7