Risk-based margining for T+2 rolling settlement uses scrip impact cost and amplified VaR to determine margins and collection timing. Stock exchanges must classify scrips into three groups using trading frequency and a rolling six month impact cost calculated from four intra-day order book snapshots; publish a common methodology; and apply differentiated margins: scrip VaR for low-impact scrips, scaled amplified VaR for higher-impact and illiquid scrips with an index VaR floor, together with continuing mark-to-market collection, discretionary adhoc margins, phased reduction of additional margins, and T+1 margin collection, with daily VaR dissemination and mandatory real-time market data.