Stage-Dependent Framework
Seed ($0-500K): Track velocity to learning. Take debt aggressively. R&D: 60-80% of burn.
Series A ($500K-2M): Track cost to acquire/serve. Start paying down revenue-critical debt. R&D: 80-120% of revenue.
Series B ($2M-10M): Track engineering efficiency. Allocate 20-25% to debt remediation. R&D: 40-60%.
Growth ($10M+): Track R&D ROI. Full economic model. Maintain PDI below 1.5. R&D: 20-35%.