How does MERN developer seniority affect hourly rate?

Seniority has a 1.5x to 2x effect on MERN developer hourly rate. Mid-level offshore India ($22 to $35/hr) to senior ($30 to $55/hr) to lead ($42 to $75/hr). The same tiers in the US run $80 to $110/hr, $120 to $160/hr, and $150 to $200/hr. The seniority premium is consistent across regions. Whether the premium is worth it depends on your MongoDB complexity and how much independent architectural decision-making the engineer needs to exercise.