What is a bill buffer, and how big should yours be?

A bill buffer is money you keep in your checking account so that bills can be paid on their due dates even when your paycheck arrives a few days late to the party. It is not savings and it is not for emergencies. It is the cushion that stops ordinary timing from causing overdrafts.

Buffer vs emergency fund

• Bill buffer: sits in checking, is used every month, and gets refilled by your next paycheck. Its job is smoothing.
• Emergency fund: sits in savings, is used rarely, and takes time to rebuild. Its job is surviving surprises.

Mixing them up is how people either drain their emergency fund to cover a timing gap, or keep far too much idle in checking.

How to size yours

There is no magic number, but there is a method. Look at one pay period and find the lowest point your balance reaches before the next paycheck lands. Your buffer needs to be at least big enough to cover that dip.

If you cannot build that all at once, build it in layers. First cover the single worst dip. Then add a margin. Then, if you want, aim for the common rule of thumb of about one month of fixed bills in checking.

How to build it without a raise

• Let the leftover from each month stay in checking instead of spending it.
• Move one bill date later so a big payment follows a paycheck rather than preceding it.
• Direct one extra paycheck a year, if you are paid every two weeks, to the buffer.

The short version

• A bill buffer smooths timing between paychecks; an emergency fund covers surprises.
• Size it to your worst dip between paydays, plus a small margin.
• Build it from leftovers and from moving bill dates, not from cutting everything.