Health factor

Reading depth

Each view includes the earlier layers; the complete engineer or auditor page is shown by default.

BeginnerCore purpose and mental modelPractitionerAdds mechanisms and economicsEngineer or auditorAdds state and verification

Dependency check

Advanced detail assumes prerequisite knowledge

Before using practitioner mechanisms or engineer and auditor checks, review any unfamiliar dependency. These paths come from canonical depends_on relationships; Web3 Academy does not track completed lessons.

Review 8 dependencies

• AssetRequired through Collateral

  1. Health factor
  2. Loan-to-value
  3. Collateral
  4. Asset

• ClaimRequired through Asset versus claim

  1. Health factor
  2. Loan-to-value
  3. Collateral
  4. Asset versus claim
  5. Claim

• TokenRequired through Asset versus claim

  1. Health factor
  2. Loan-to-value
  3. Collateral
  4. Asset versus claim
  5. Token

• Asset versus claimRequired through Collateral

  1. Health factor
  2. Loan-to-value
  3. Collateral
  4. Asset versus claim

• Claim tokenRequired through Lending pool

  1. Health factor
  2. Loan-to-value
  3. Lending pool
  4. Claim token

• CollateralRequired through Loan-to-value

  1. Health factor
  2. Loan-to-value
  3. Collateral

• Lending poolRequired through Loan-to-value

  1. Health factor
  2. Loan-to-value
  3. Lending pool

• Loan-to-valueDirect prerequisite

  1. Health factor
  2. Loan-to-value

A health factor is a protocol-defined ratio or score that summarizes how much liquidation-adjusted collateral supports a borrower's debt.

Category: LendingSplit balance category cue

System record

Start with the economic purpose, participants, resources, and entitlements before studying implementation detail.

Why it exists

Health factors turn multiple collateral, debt, price, and threshold inputs into an operational signal for borrowing restrictions and liquidation eligibility.

Traditional-finance analogy

Collateral coverage or maintenance-margin ratio is the closest comparison recorded for this concept.

Where the analogy stops

• There is no universal DeFi health-factor formula, threshold, weighting, or safety interpretation across protocols.
• On-chain scores can change with oracle updates and accrued interest and can trigger permissionless liquidation immediately under configured rules.

Main actors

• ActorBorrower
• ActorLending pool or creditor
• ActorOracle
• ActorLiquidator
• ActorGovernance or risk administrator

Assets and claims

Assets — controlled or transformed resources

Assets are resources the mechanism moves, holds, values, or transforms.

• AssetLiquidation-adjusted collateral value
• AssetDebt value

Claims — entitlements and corresponding dependencies

Claims are rights to value, repayment, redemption, control, or another party's performance; each depends on an obligation or system that must honor it.

• ClaimBorrower debt obligation
• ClaimCreditor's liquidation entitlement

A health factor summarizes how much liquidation-adjusted collateral supports a borrower’s debt under one protocol’s rules.

Why it exists

A position can contain several collateral and debt assets with different prices and thresholds. A health factor compresses that state into an operational signal for risk-increasing actions and liquidation. Compression is convenient, but it can hide which asset or assumption drives the result.

Traditional-finance analogy

A collateral-coverage or maintenance-margin ratio is a useful analogy. Unlike a periodic broker call, a DeFi score can change with each oracle or interest update and can permit immediate permissionless liquidation. There is no universal formula, threshold, weighting, or “safe” health factor across protocols.

One model, not a universal formula

liquidationAdjustedCollateralValueUsd
= Σ(collateralValueUsd_i × liquidationThreshold_i)

healthFactor
= liquidationAdjustedCollateralValueUsd / totalDebtValueUsd

Both numerator and denominator use USD here, so the result is unitless. In the Aave V3 model documented below, a value below 1 is liquidatable. Another protocol can define different inputs, factors, or boundaries. Zero debt should be represented as debt-free, not evaluated through division by zero.

Step-by-step health-factor calculation

1. Inventory every eligible collateral amount, debt amount, price, decimal scale, and protocol mode.
2. Convert each collateral position to the common reference unit and apply its liquidation threshold.
3. Convert each debt position to the same reference unit, including accrued interest.
4. Sum liquidation-adjusted collateral and total debt without mixing units or stale observations.
5. Divide adjusted collateral by debt, or return an explicit debt-free state when debt is zero.
6. Compare the result with the protocol’s liquidation boundary and preserve the components needed to explain the score.

State and interpretation

Table: State and interpretation

Change	Health factor, all else equal	Why
Add eligible collateral	Rises	Adjusted collateral value rises
Repay debt	Rises	Denominator falls
Borrow more	Falls	Denominator rises
Collateral price falls	Falls	Numerator falls
Debt asset price rises	Falls	Denominator rises
Interest accrues	Falls	Debt grows
Governance lowers a threshold	Falls	Credited liquidation value falls

A high ratio does not prove exit liquidity, oracle quality, contract safety, or future price stability. It measures only what its formula includes.

Flows and loss allocation

Information flow carries prices, balances, thresholds, special modes, and debt indices into the score. Control flow identifies governance and oracle authority. Capital flow begins only when the borrower adjusts the position or liquidation executes. Claim flow is the borrower debt and the pool’s conditional right to seize collateral; calculating the score alone creates no new claim. Return flow does not originate in the ratio, although borrower interest can increase debt and thereby reduce the score. Risk flow begins with an adverse price, interest, parameter, or data change and reaches the borrower through seized collateral; reserves, backstops, or suppliers bear any residual bad debt under explicit rules.

Engineer or auditor lens

Reconstruct every component independently. Test zero debt, zero prices, mixed decimals, multiple collateral and debt assets, weighted thresholds, isolation or correlation modes, stale or negative data, accrued interest, rounding at 1, same-block changes, and consistency with the actual liquidation check. The UI and settlement contract must not use divergent formulas or state.

Aave’s health-factor and liquidation documentation states its weighted-threshold formula and boundary. It was reviewed 2026-08-09 as an Aave-specific example, not as a universal lending definition or guarantee that a position above 1 cannot lose value.

Common misunderstandings

• “Every protocol liquidates below one.” The formula and threshold are protocol-defined.
• “A health factor is a probability of default.” It is an operational coverage ratio or score.
• “Above the boundary means safe.” Price gaps, stale oracles, liquidity, code, and governance remain.

Next follow the state transition in lending liquidation.

Machine-readable model

Key equations

Canonical expressions come from the structured concept record. KaTeX renders the notation, while the plain-text expression and variable table keep its meaning and units inspectable without JavaScript. Read the narrative above for the model's domain, assumptions, and rounding rules.

1. Equation 1

   $$\mathrm{healthFactor} = \frac{\mathrm{liquidationAdjustedCollateralValue}}{\mathrm{debtValue}}$$

   Plain-text equation: healthFactor = liquidationAdjustedCollateralValue / debtValue

   Variables and units for equation 1

   Symbol	Meaning	Unit
   healthFactor	Health Factor	dimensionless ratio
   liquidationAdjustedCollateralValue	Liquidation Adjusted Collateral Value	selected valuation unit (for example, USD)
   debtValue	Debt Value	selected valuation unit (for example, USD)

Assurance contract

Security properties

These structured statements define desired behavior. Their stable IDs can bind tests, invariants, specifications, audit findings, or proof results without turning descriptive review advice into an assurance claim.

Desired · not evaluated: No test, audit, or proof result is implied until scoped evidence is linked to this property.

1. SP-01Desired · not evaluated

   Every input, weight, threshold, price, unit, and special mode in the score is explicit

2. SP-02Desired · not evaluated

   Zero debt is handled as debt-free rather than an unsafe division

3. SP-03Desired · not evaluated

   Liquidation eligibility is derived from the same reconciled state used for settlement

4. SP-04Desired · not evaluated

   Borrowing and collateral withdrawal cannot move a position past configured constraints unnoticed

Prerequisites

Direct dependencies recorded by this concept's canonicaldepends_on relationships.

• Loan-to-valuePath 17

  Loan-to-value is the ratio of debt value to collateral value under a stated price, eligibility, and aggregation model.

Learn next

Concepts that directly depend on this one, ranked by the recommended learning path. Check each page for additional prerequisites.

• Lending liquidationPath 45

  Lending liquidation repays or assumes unsafe debt and transfers or sells collateral under protocol rules to restore solvency or limit further loss.

Knowledge check

Quiz

Answer in your own words, then open the model answer.

What problem does Health factor exist to address?

Model answer

Health factors turn multiple collateral, debt, price, and threshold inputs into an operational signal for borrowing restrictions and liquidation eligibility.

Mark as understood