In general, long-term credit ratings have default probabilities like: A category: less than 0.25% chance of default B category investment grade: 0.25%-1-7.5% chance of default B category speculative grade: 7.5%-20% chance of default C category: 20%-34% chance of default D category: in default It is important to remember that these are probabilities. The table should be used as a way of comparing bonds of similar rating vs. bonds rated differently.