Discount Formula

The discount a swapper pays is derived from the opportunity cost of waiting in Lido's withdrawal queue.

Formula

discount   = stEthAmount × apyBps × waitSeconds / (10_000 × SECONDS_PER_YEAR)
grossOut   = stEthAmount − discount
feeAmount  = grossOut × feeBps / 10_000
userOut    = grossOut − feeAmount

Variable	Description
stEthAmount	Input amount of stETH
apyBps	Expected ETH staking APY in basis points (e.g. 400 = 4%)
waitSeconds	Expected Lido withdrawal wait time in seconds
feeBps	Protocol fee in basis points (default 0)

Example

• stETH amount: 10 ETH
• Expected APY: 4% (apyBps = 400)
• Expected wait: 14 days (waitSeconds = 1_209_600)

discount  = 10 × 400 × 1_209_600 / (10_000 × 31_536_000)
          = 10 × 0.04 × (14/365)
          ≈ 0.01534 ETH

userOut   = 10 − 0.01534 = 9.98466 ETH (WETH)

The swapper receives ~9.985 WETH instead of waiting ~14 days for 10 ETH.

Slippage protection

Call getSwapQuote(stEthAmount) first to get the expected userOut. Pass this value as minEthAmountOut when calling swapStETHToWETH to protect against parameter changes between quote and execution.

Parameter bounds

• apyBps is capped at 10_000 (100%)
• waitSeconds is capped at SECONDS_PER_YEAR (365 days)
• These bounds guarantee grossOut ≥ 0