Once the insurer declares an annual Simple Reversionary Bonus, it becomes 'vested' — guaranteed to be paid out on death or maturity, but not before. Vested Bonus is the running total of all such annual bonuses credited to your policy so far.
For LIC endowment plans, vested bonus is calculated as: (declared rate per ₹1,000 SA) × (Sum Assured / 1,000) × (years vested). The rate is reset every financial year by LIC's actuarial committee — historical rates have ranged from ₹40–₹55 per ₹1,000 SA for most endowment plans in recent years.