[header] How to know when to use your rainy day fund [title] Check if the expense is necessary. [step] You didn't build up a rainy day fund simply because you might want to buy new clothes or new appliances. Check if the expense is absolutely necessary. 
[substeps] Do you need something in order to do your job? If so, then it probably is a necessary expense. Car repairs or a new laptop are probably necessities because you can't work without them.