What Is Flash Loan?
A flash loan is an uncollateralized loan that is borrowed and repaid within a single blockchain transaction. If the loan isn't repaid by the end of the transaction, the entire operation reverts as if it never happened — the lender bears zero risk. This enables massive capital deployment (millions of dollars) with zero upfront capital.
How Flash Loan Works
Flash loans are enabled by blockchain atomicity: every operation within a transaction either succeeds entirely or fails entirely. A flash loan transaction might: borrow $50M → exploit a price difference across DEXs → repay $50M + fee → pocket the profit. If any step fails (e.g., the arbitrage isn't profitable enough), the entire transaction reverts and only the gas fee is lost.
Why It Matters for Traders
Flash loans are a powerful tool for arbitrageurs and liquidators who can execute profitable strategies with zero capital risk. However, they've also been the mechanism behind many DeFi exploits — attackers use flash loans to temporarily manipulate oracle prices or exploit logic bugs in protocols. Understanding flash loans helps traders recognize when unusual market activity (sudden liquidity shifts, oracle deviations) might be flash loan-driven.
How It Shows Up for Perps Traders
Even if you mainly trade CEX perps, flash loan still matters when you hedge with spot, move collateral across chains, or compare DEX perps funding to CEX funding. Thin pool depth and oracle lag can widen the gap between the index you hedge and the book you trade.
Formula and Worked Example
Example numbers only (not a live quote).
Suppose you compare a spot bag and a short perp hedge. If the hedge notional is $5,000 and the spot bag drifts 2% while the hedge mark moves 1.2%, the residual basis is 0.8% of notional, or $40 on that $5,000 book. That gap is the cost of an imperfect hedge, separate from funding.
Common Mistakes
- Treating a single print of flash loan as a trade signal without checking funding, open interest, and your liquidation price.
- Mixing venue conventions (coin-margined vs USDT-margined, cross vs isolated) and reading the wrong mark.
- Copying example numbers from a glossary into live size without checking the current book depth and fee schedule.
- Ignoring related terms that change the meaning of the print on a given day.
