Lending effective APY calculator — net of fees

A quoted lending APY is a useful starting point, but it is not the same as the return that reaches the depositor. In DeFi lending markets such as Aave or Compound, part of the interest stream can be diverted to protocol reserves before it is credited as lender income. That means the headline figure can overstate the practical result, especially when the comparison is between markets with similar posted rates but different fee structures. The data that matters most is not only the advertised yield, but how much of that yield survives each layer of drag.

Transaction costs add another gap between gross and realized performance. Gas to enter and exit a position is typically fixed in dollar terms, so it weighs more heavily on smaller deposits and shorter holding periods. Compounding also changes the outcome: the same nominal rate can translate into different realized returns depending on how often earnings are reinvested. Taken together, protocol fees, gas, and compounding frequency turn a simple APY quote into a more complex net-yield calculation. That net figure is the more practical lens when comparing DeFi lending with other yield opportunities that carry different cost and reinvestment mechanics.

The calculator begins with the deposit amount, which is the principal earning interest over the selected holding period. It then applies the stated APY to estimate gross interest before any deductions. From that gross interest, it subtracts the protocol fee on yield, representing the share retained by the lending protocol rather than passed through to the lender. Next, it includes gas in and gas out as one-time costs, since opening and closing the position usually requires on-chain transactions. The result is then adjusted for the holding period and the chosen compound frequency, because a shorter time horizon or less frequent reinvestment reduces the benefit of compounding. Finally, the output is broken into components that can be compared directly: gross yield, protocol fee paid, gas drag, net yield, and effective APY. This structure helps separate the posted rate from the realized economics of the position.

This calculator is most useful when the headline APY alone does not tell the full story. Traders often use it to compare two lending markets that advertise similar yields but differ in reserve factors, withdrawal costs, or compounding assumptions. It is also relevant before opening a smaller lending position, where fixed gas costs can absorb a meaningful share of the interest and make the posted APY look more attractive than the realized outcome. The same logic applies to short holding periods: if the position is not open long enough, entry and exit costs can outweigh much of the earned yield.

It also helps when evaluating whether a quoted lending rate remains compelling after protocol fees and transaction costs are included. In that sense, the tool is less about the headline number and more about isolating the return that remains after all known drag. It is somewhat less informative for very large positions, where gas becomes negligible relative to principal, and for variable-rate lending markets where the quoted APY may change quickly after deposit. In those cases, the calculation still frames the cost structure, but the rate assumption itself may shift before the holding period is complete.

Consider a lender depositing $1,000 into a market quoting a 5% stated APY, with a 10% protocol fee on yield. The position is held for 365 days, rewards are compounded monthly, and the user pays $8 to enter and $8 to exit. Starting from the headline rate, the gross annual interest is $50 on the $1,000 deposit. The protocol then keeps $5, which is 10% of that interest, leaving $45 before transaction costs are considered.

The next adjustment is gas. With $16 total gas across entry and exit, the transaction drag equals 1.6% of the original deposit. Subtracting that cost from the post-fee interest leaves a net yield of $29 for the year. Expressed as a rate on the original $1,000, that works out to an effective APY of about 2.9% net. The example shows the gap between a 5.0% gross lending quote and the realized return after protocol fees and fixed on-chain costs are included. The headline yield remains the starting point, but the net result is what defines the actual economics.

A frequent mistake is treating the stated APY as if it were the amount fully credited to the lender. In practice, protocol reserve factors can reduce the share of interest that reaches the depositor, so the posted figure can overstate realized income. Another common error is ignoring gas in and gas out. Because these costs are fixed rather than proportional, they can dominate returns on smaller deposits or on positions held only briefly.

Users also often mix up APR and APY, which can distort the role of compounding. If a quoted rate already reflects compounding and that effect is added again, the result is overstated; if compounding is ignored entirely, the result can be understated. A related issue is assuming that compounding happens automatically at the same cadence as the quote. Some lending positions require manual reinvestment, while others do not compound in the way the headline number implies. Finally, holding period is easy to overlook. A short duration can make exit costs large relative to the interest earned, so a position that looks attractive on an annual basis may produce a much weaker net result over the actual time it is held.

Effective lending yield sits alongside several related ideas that shape the full economics of a DeFi position. When lending is paired with borrowing, health factor and loan-to-value become relevant because collateral risk can alter the practical return profile. A lending rate may appear attractive in isolation, but the broader position can carry balance-sheet risk that changes how traders interpret the yield.

It is also important to separate protocol fees from gas fees. Both reduce realized return, but they operate differently: protocol fees are tied to the interest stream, while gas is a transaction-layer cost paid to enter and exit. Compound interest concepts help explain why compounding frequency changes the gap between a nominal rate and the effective result over time. This is closely related to APR/APY conversion, which is useful when comparing rates quoted under different compounding assumptions. Together, these concepts provide a clearer framework for evaluating whether a lending opportunity is attractive on a gross basis, on a net basis, or only under a specific holding period and transaction-cost profile.