Margin Trading System Development

Margin Trading System Development

Margin trading is trading with borrowed funds. Trader deposits collateral (margin), gets leverage (2×, 5×, 10×), and can trade larger volume. Exchange earns on funding rate / interest. Task: build system that won't allow losses greater than collateral (otherwise exchange bears risk).

Types of Margin Trading

Isolated Margin

Each position has its own collateral. Risk limited to specific position collateral — other positions unaffected during liquidation.

Cross Margin

All user positions use common collateral pool. Profitable positions support losing ones. Liquidation occurs when entire balance goes negative.

Liquidation Price Calculation

For Long position with isolated margin:

func CalculateLiquidationPrice(pos IsolatedPosition, config MarginConfig) Decimal {
    maintenanceMarginAmount := pos.EntryPrice.Mul(pos.Quantity).Mul(config.MaintenanceMarginRate)
    lossAtLiquidation := pos.InitialMargin.Sub(maintenanceMarginAmount)
    priceDropAllowed := lossAtLiquidation.Div(pos.Quantity)
    
    if pos.Side == Long {
        return pos.EntryPrice.Sub(priceDropAllowed)
    } else {
        return pos.EntryPrice.Add(priceDropAllowed)
    }
}

Example: Long BTC, entry $42,000, leverage 10x

• Initial Margin: $42,000 / 10 = $4,200
• Maintenance Margin Rate: 0.5%
• Liquidation price: $38,010

Liquidation Engine

Liquidation must happen quickly: during sharp market moves multiple users' positions can hit liquidation price simultaneously.

Levels of protection:

• Level 1: Partial liquidation — close part of position to raise margin
• Level 2: Full liquidation — position fully closed by liquidation engine
• Level 3: Insurance fund — if liquidation price worse than bankruptcy price, difference covered by insurance fund
• Level 4: Auto-Deleveraging (ADL) — if insurance fund insufficient, profitable positions forcefully closed

Insurance Fund

When sharp moves cause liquidation at worse price than liquidation price, remaining loss covered by Insurance Fund — pool formed from liquidation fees.

ADL (Auto-Deleveraging): if Insurance Fund exhausted, forcefully close most profitable positions to cover loss. Harsh measure used as last resort.

Funding Rate for Perpetual Contracts

Perpetual futures don't have expiration. Price pegged to spot through funding rate mechanism:

func (fe *FundingEngine) CalculateRate(pair string) Decimal {
    markPrice := fe.getMarkPrice(pair)
    indexPrice := fe.getIndexPrice(pair)  // spot price from major exchanges
    
    // Premium = (mark - index) / index
    premium := markPrice.Sub(indexPrice).Div(indexPrice)
    
    // Funding Rate = Premium + clamp(InterestRate - Premium, -0.05%, 0.05%)
    interestRate := Decimal("0.0001")  // 0.01% base rate
    
    clampedDiff := Clamp(
        interestRate.Sub(premium),
        Decimal("-0.0005"),
        Decimal("0.0005"),
    )
    
    return premium.Add(clampedDiff)
}

Long pays if rate > 0 (mark > index), receives if rate < 0.

Mark Price vs Last Price

Liquidation based on mark price (aggregated price from multiple exchanges), not last trade price. Otherwise possible manipulation: large trader makes small trade at extreme price and triggers liquidations.

func (fe *FundingEngine) GetMarkPrice(pair string) Decimal {
    // Median price from Binance, OKX, Bybit
    prices := []Decimal{
        fe.binanceFeed.GetPrice(pair),
        fe.okxFeed.GetPrice(pair),
        fe.bybitFeed.GetPrice(pair),
    }
    sort.Slice(prices, func(i, j int) bool { return prices[i].LessThan(prices[j]) })
    return prices[1]  // median of 3
}

Development Timeline

Full margin trading system: 4–6 months.