The base salary of US representatives/senators is about $14,500 per month. One of the typical health plans they may choose is Blue Cross/Blue Shield. Their premium is about $430 per month, which is about 3% of their salary. This includes family coverage.
The average Social Security recipient receives $1177 per month. Their cost for Medicare Part B is about $100 per month, which is about 8% of their monthly income from Social Security. This is single coverage.
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Disclaimer: Any misrepresentations are due to ignorance rather than malice aforethought. Please feel free to let me know if I have indeed misinterpreted the reference data.