What you read online was wrong. The percent for a garnishment is set by law, and essentially about 25% of your after tax income will be lost.
You need to treat this an emergency and see a lawyer first thing in the morning. There are two possibilities: (1) If there is a defect in the original case, you may be able to traverse the garnishment and seek to atack the judgment, or (2) you may bankrupt on the debt. (There also could be a defect in the garnishment papers or service to allow a traverse).
But unless you get a lawyer and do one of those things, they will be taking a quarter of your pay.
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The exempt amount is 30 times the minimum wage, or 30 x $7.25, which is $217.50. Above that, they can garnish, up to a maximum of 25% of your net pay. If you have a 36-hour week, that would be $296.64, which is above the exempt amount and leaves potentially 25% available for garnishment. The exact numbers will depend on what is taken out for taxes.
As discussed elsewhere, you could fight the garnishment on procedural grounds regarding a judgment which was obtained through invalid means. Of course, that might cost money for legal fees and might not be easy. It is possible that the wrong person was served with papers (that happens), or maybe you had a former roommate or relative accept service at a house you had already moved out of, or maybe there is some other reason service might have been invalid. However, many people don't understand the process and do remember getting served with papers but do not understand the process.