Tier Categories are the three-tier classification used in Impact IRR attribution to group investments in the capital stack by similar risk/return profile: - *Tier 1: Below-Market-Rate Impact Capital (BIC) debt and equity — first-loss position. - Tier 2: Equity and equity-like investments, preferred stock. - Tier 3:* Debt and debt-like investments, common stock. Attribution of impact return is calculated within tiers — an investment's pro-rated share is determined by dividing its capital by the total capital in the same tier.