Mass gambling wins/losses are treated differently than Federal or any other state. Mass W2G lottery/keno wins are also treated differently than a Mass casino win. The only Mass lottery/keno loss that can be deducted on Mass tax returns are the costs of winning tickets. If a W2G was rec'd from a Mass casino, request your win/loss statement(s) from Mass casino's to determine your Mass overall gambling win/loss; your W2G win will be included in your statement total. If your Mass statement(s) total a win, you do not have a loss to deduct, nor will you have proof of any gambling loss. If your Mass statement(s) total a loss, then you can deduct the amount of that total Mass casino loss and keep the win/loss statements as your tax documentation. For Mass tax, cannot deduct casino losses from any casino's outside of Mass.
