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Hi Everyone,I?m fetching FX vols from Bloomberg: ATM, RiskResersal 10/25 Delta and Butterfly 10/25 Delta.For each of these quotes, I get a mid / bid / ask.i.e.VolQuote; Mid ; Bid ; AskUSD/IDR 1W ATM; 3.137; 1.637; 4.637USD/IDR 1W 25_Delta_RR; 2.287; 0.301; 4.273USD/IDR 1W 25_Delta_BF; -0.0475; -2.615; 2.519USD/IDR 1W 10_Delta_RR; 3.748500 ; -1.065000 ; 8.562000USD/IDR 1W 10_Delta_BF; 2.443500 ; -1.657000 ; 6.544000 From these quotes, I want to get my vol surface expressed in delta (i.e. I want to get ATM, 10/25DeltaCall and 10/25DeltaPut).To calculate the Mid vols, I use the standard formulas:25_Delta_Call_mid = Butterfly_25_Delta_mid + (Risk_Reversal_25_mid / 2) + ATM_mid25_Delta_Put_mid = Butterfly_25_Delta_mid - (Risk_Reversal_25_mid / 2) + ATM_midSo far, so good. That works. No surprise.When I apply the same formulas to, let say, calculate the Asks. It does not work anymore; I?m getting negative vols.Any idea how people work these things out?thanks for your helpregards

Your quote on ATM shows that the bid-ask spread is 3% vol (bid-to-mid 1.5% and mid-to-ask another 1.5%).Could you not use this information to apply the same spreads for the call and the put ?