Base reward per wave

Base_Reward = 15 * wave_number.

Effective wave yield

Current_Wave_Yield = Base_Reward * (1.0 + 0.2 * multiplier_level) * (1.0 + cloud_farm_bonus + weapon_bonus).

Upgrade cost scaling

Next_Upgrade_Cost = 500 * POWER(1.18, current_multiplier_level).

Path A (direct save)

Waves_Path_A = (Target_Expansion_Cost - Current_Cash) / Current_Wave_Yield.

Path B (upgrade then save)

Waves_Path_B = waves_to_buy_upgrade + waves_to_save_post_upgrade.