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Cryptocurrency & Blockchain

Lending Protocols: Aave and Compound

Overcollateralization, cToken Accounting, and the Math of Liquidations — A TLDR Primer

DeFi lending protocols look simple on the surface — deposit crypto, earn yield, borrow against collateral — until you try to understand *why* the interest rate just jumped, what a health factor actually measures, or how a liquidation bot just took 10% of someone's position in a single block. If you've hit that wall, this guide is for you.

**Lending Protocols: Aave and Compound** is a concise primer that walks you through the real mechanics of the two most important decentralized lending markets. You'll learn how pooled liquidity works without a bank in the middle, how the kinked utilization curve drives supply and borrow rates up and down automatically, and how Compound's cTokens and Aave's aTokens track your deposit's growing value as a receipt token rather than a balance. The guide then covers collateral factors, liquidation thresholds, and the full math of getting liquidated — with a worked numerical example so the numbers make sense before you risk real money.

This book is written for early college students, self-taught developers entering the Web3 space, and anyone who wants a clear decentralized finance protocol study guide without wading through whitepapers or Discord lore. The final two sections compare Aave and Compound on flash loans, stable-rate borrowing, isolation mode, and governance — then survey real exploits and failure modes so you know what to check before you deposit.

Short by design. No filler. Read it in an afternoon and actually understand what's happening on-chain.

What you'll learn
  • Explain how a decentralized lending pool replaces a traditional bank
  • Read and interpret supply APY, borrow APY, and utilization rate
  • Understand cTokens and aTokens as interest-bearing receipts
  • Calculate collateral factors, health factors, and liquidation thresholds
  • Compare Aave and Compound's design choices and risk tradeoffs
  • Identify the main risks: smart contract bugs, oracle manipulation, and liquidation cascades
What's inside
  1. 1. What a DeFi Lending Protocol Actually Is
    Introduces pooled lending, overcollateralization, and why a bank-free credit market needs different rules than a traditional bank.
  2. 2. Interest Rates, Utilization, and the Kink
    Explains how supply and borrow rates are determined algorithmically by pool utilization, including the kinked rate curve both protocols use.
  3. 3. cTokens and aTokens: Receipts That Earn Interest
    Breaks down how Compound's cTokens and Aave's aTokens track deposits, with worked conversions between underlying and receipt tokens.
  4. 4. Collateral, Health Factor, and Liquidations
    Covers collateral factors, liquidation thresholds, and the math of getting liquidated, with a full numerical example.
  5. 5. Aave vs. Compound: Design Choices That Matter
    Compares the two protocols on flash loans, stable rate borrowing, isolation mode, governance, and risk parameters.
  6. 6. Risks, Failures, and Why It Still Works
    Surveys real exploits and market events — oracle attacks, bad debt, and liquidation cascades — and what users should check before depositing.
Published by Solid State Press
Lending Protocols: Aave and Compound cover
TLDR STUDY GUIDES

Lending Protocols: Aave and Compound

Overcollateralization, cToken Accounting, and the Math of Liquidations — A TLDR Primer
Solid State Press

Lending Protocols: Aave and Compound

Overcollateralization, cToken Accounting, and the Math of Liquidations — A TLDR Primer

Copyright © 2026 Solid State Press.

Published by Solid State Press.

All rights reserved. No part of this book may be reproduced or transmitted in any form without prior written permission, except for brief quotations in critical reviews and educational use.

Part of the TLDR Study Guides series.

Contents

  1. 1 What a DeFi Lending Protocol Actually Is
  2. 2 Interest Rates, Utilization, and the Kink
  3. 3 cTokens and aTokens: Receipts That Earn Interest
  4. 4 Collateral, Health Factor, and Liquidations
  5. 5 Aave vs. Compound: Design Choices That Matter
  6. 6 Risks, Failures, and Why It Still Works
Chapter 1

What a DeFi Lending Protocol Actually Is

Imagine a savings account that pays you 8% interest — not because a bank decided to offer it, but because an algorithm matched your deposit to a borrower's loan in real time, with no loan officer, no credit check, and no headquarters. That is the basic promise of a DeFi lending protocol.

DeFi (short for decentralized finance) refers to financial services that run on a public blockchain — most commonly Ethereum — through smart contracts: self-executing programs that hold funds and enforce rules without any company or person controlling them. Aave and Compound are the two largest DeFi lending protocols by assets. Together they have managed tens of billions of dollars in deposits at their peaks.

How a Lending Pool Works

A traditional bank takes deposits from customers and issues loans to other customers, pocketing the spread between the rate it pays depositors and the rate it charges borrowers. The bank knows who its customers are, checks their credit history, and can take them to court if they default.

A DeFi protocol can do none of those things. Borrowers are anonymous wallet addresses. There is no legal system the protocol can appeal to, and no way to garnish wages or seize a car. So the entire model shifts.

Instead of bilateral loans (one lender, one borrower), Aave and Compound use a lending pool: a single smart contract that aggregates deposits from many lenders. When you deposit 10 ETH, it goes into the same pool as everyone else's ETH. Borrowers draw from that pool. Interest paid by all borrowers flows back into the pool and is distributed proportionally to all depositors. You are not matched to a specific borrower — you are a fractional owner of the whole pool's yield.

This design has one major implication: the pool cannot verify creditworthiness, so it cannot extend unsecured loans (loans backed only by a promise to repay). Instead, every loan must be overcollateralized — the borrower must lock up more collateral than they are allowed to borrow.

Overcollateralization: The Core Rule

About This Book

If you're a college student trying to understand DeFi protocols for a fintech or blockchain course, a self-taught crypto investor who wants DeFi borrowing and lending explained simply, or a developer stepping into Web3 and hitting a wall on how interest rates and collateral actually work — this book is for you. It also suits curious high schoolers and anyone who opened a Compound or Aave dashboard and immediately felt lost.

This is a decentralized finance protocol study guide that covers the mechanics behind pooled liquidity, how cTokens and interest rates work in DeFi, the math of blockchain lending overcollateralization, and crypto collateral liquidation explained for beginners with real numbers. It walks through how Aave and Compound lending work — from the utilization kink to health factors — without assuming any prior finance background. Short by design, no filler.

Read straight through in order, since each section builds on the last. Work through every Example block when you hit it, then use the problem set at the end to confirm you've got it.

Keep reading

You've read the first half of Chapter 1. The complete book covers 6 chapters in roughly fifteen pages — readable in one sitting.

Coming soon to Amazon