What is a forward contract?
A forward contract is an agreement between two parties to buy or sell an asset at a fixed price on a future date. Between the time the trade is accepted and the time the trade settles, the price of the underlying asset may move up or down. Companies use forwards to protect themselves from swings in commodity prices, interest rates, and FX rates.
Why margin exists
That agreement is only a promise: nothing forces either side to keep it. A forward always finishes with a winner and a loser: the price moves, one side ends up owing the difference, and the other waits to collect it. If the loser walks away, the winner takes the loss.
Neither side knows in advance which one it will be. Each needs protection from the other, and each sizes up its counterparty, the party on the other side of the trade, with the same two questions. Will it still be around when the purchase comes due? If the market moves against it, will it still honor the price it locked?
The traditional protection is credit: one side investigates the other until the promise feels safe, then keeps watching for the life of the trade. Margin protects differently: money set aside in advance stands behind whoever makes the promise. The market calls that money collateral, and it comes in two layers with two separate jobs. Variation margin covers the moves that happen along the way, and initial margin covers the counterparty that walks away.
What is variation margin?
A single trade shows both layers at work. One side agrees to buy €5.0 million one month from now, and the other agrees to sell, at a price fixed today: $1.20 per euro. In dollars, the deal locks at $6.0 million, no matter where the exchange rate goes.
A clearinghouse stands between the two sides of the trade. It takes collateral from the buyer and collateral from the seller, and holds each in a margin account.
One day later, the euro climbs to $1.23. The same €5.0 million now costs $6.15 million on the open market. The buyer's fixed price of $6.0 million now beats the market by $150,000. Variation margin is that gain, paid out the day it appears: $150,000 moves from the seller's margin account into the buyer's.
Tomorrow the rate moves again, and the payment flows again, wherever the market sends it next. Each day's change in value gets paid the day it happens. Debts between the two sides never grow older than one day, and losses never pile up quietly until the purchase comes due.
What is initial margin?
The daily payments handle the counterparty that stays and pays. Initial margin handles the counterparty that leaves. Think of it as a security deposit on an apartment. The clearinghouse skips the months-long investigation the same way a landlord with a deposit in hand skips the background check.
Initial margin is the trade's security deposit: money both sides put up before the trade begins. Its size answers one question: how far the price can move in the time it takes the clearinghouse to shut a dead trade down. The deposit never needs to cover the full $6.0 million. It only needs to cover the distance the rate can travel between the last daily payment and the shutdown. On this trade, each side puts up $300,000, five percent of the $6.0 million.
Sizing the deposit
Every corner of the derivatives market sizes that deposit with a model, and the models differ by venue. CME runs the world's largest market for futures, the forward's exchange-traded cousin, clearing 28 million contracts a day. Its SPAN framework tests each trade against a grid of imagined market shocks. The worst imagined loss sets the deposit.
LCH clears most of the world's interest-rate swaps, contracts like the forward but built on interest payments, over $500 trillion of them in the final quarter of 2025 alone. It sizes deposits by replaying roughly ten years of real market history against today's trades, hunting the rare and severe move at the edge of that record. The deposit must survive that move.
Trades that never reach a clearinghouse, struck directly between two institutions, fall under the uncleared margin rules. Both sides put up a deposit there too, computed most often with SIMM, a standard model published by ISDA, the derivatives industry's trade association. The arithmetic differs. The question never does: how far the price can move in the time it takes to shut a dead trade down.
Suppose the buyer walks away the day the trade is struck. By the time the clearinghouse shuts the trade down, the euro has slid to $1.15. The same euros now cost only $5.75 million on the open market. The buyer's locked price now trails the market by $250,000.
The clearinghouse shuts the trade at the market price, takes the $250,000 hole out of the buyer's $300,000 deposit, and pays the seller in full. The seller collects without a lawsuit, a negotiation, or a claim on anyone's estate. The deposit exists for exactly this moment.
What margin replaces
The two questions from the top now have answers. The counterparty can vanish tomorrow. Every move to date has already been paid out, and the deposit covers whatever the last day brings. The counterparty's credit can stay a mystery. No one lent anyone anything.
No credit file opens. No committee meets, and no lawyer drafts a settlement. Instead, two deposits, a daily payment, and a shutdown rule do the credit check's old job.
The result is a market that runs on collateral instead of credit.