Gross burn is the total amount of money you are spending per month. Net burn is the amount of money you are losing per month. So if your costs are $500,000 per month and you have $350,000 per month in revenue then your net burn (500–350) is equal to $150,000. The reason that most investors quickly zero in on net burn is that if you have $3 million in your bank account and have a net burn of $150,000 per month you have more than 18 months of cash left provided your net burn stays constant. Conversely if you’re burning $600,000 per month (yes, some companies do) then you only have 5 months of cash left.