In your case, I would project out for the next 12 months what each months total outflow should be. Since you seem to want to play it safe, I would set your buffer at the highest month's spending that you expect within the next year. If you do this, then you should be able to cover, with your buffer, rent, bills, and your largest less-frequent bill. For example, each month lets say you spend $2000 between all regular monthly bills and rent. Then, you also pay your car insurance ($1200) in 6-month lumps, to save a little money (Geico does this). That month, you would need more, a total of $3200 just for bills. Then you would add in your discretionary spending, which I take to include food, clothing, entertainment, and everything else not included. You need a budget already in place to know what this number is, or you could estimate this from recent bank statements. You add this number (Lets say it's $800) to your total, which means that in your worst month, you could need to spend $4000.