Need to sell HDB but haven't hit MOP, what happens?

You generally cannot sell on the open market before MOP, full stop, that's the rule and there's no "penalty payment" workaround to sell early to a buyer. BUT there are specific exceptions where HDB may allow early sale, and given your family circumstances you should appeal directly to HDB. Real cases I know that got approved: divorce, financial hardship (retrenchment, unable to service loan), medical grounds, or emigration. In these HDB can require you to sell back to them or approve an open-market sale. Steps: 1) Write in to HDB with documentation of your circumstances, be specific and honest. 2) If it's financial, also talk to your bank/HDB about loan deferment as an interim measure while you sort things out. 3) Don't try to sublet the whole flat to escape payments before MOP, whole-flat rental isn't allowed pre-MOP and you'll get in trouble. Appeal first, they do assess genuine hardship case by case.