Final answer:
The yearly income threshold for mandatory Medisave contributions by self-employed individuals in Singapore is $6,000.
Step-by-step explanation:
The salary limit before a self-employed individual is required to pay Medisave contributions in Singapore is $6,000 per year, not per month. This means if the net trade income is more than $6,000 annually, the individual is obliged to contribute to Medisave.
The information provided in the question with various income brackets and corresponding amounts doesn't correspond directly to Medisave requirements, but rather seems to illustrate different tax brackets or deductions, which may be relevant for understanding how such contributions are calculated within the context of broader fiscal responsibilities.