How do you plan for sick days?
Everyone will get sick and miss work. It's a fact of life.
As a 1099, you likely get paid hourly, which means you don't get paid when you stay home and stop working. Then your check is smaller than you expected, which is never fun.
So what should you do?
Simple: bake it into your billable hours projection.
If you worked every business day, you'd bill something like 2000 hours per year.
If you know you'll take vacation, subtract that estimated amount. Say 160 hours (4 weeks). You're down to 1840 billable hours.
Now, say you expect to miss at least two weeks of work due to various sicknesses, doctors' appointments etc, subtract 80 hours.
Now you're down to 1760 hours per year.
Plan your income and personal finances around only billing 1760 hours.
If you happen to work more, save that extra money as a sick day fund.
If you find that that's not enough money, you need to work more hours (i.e. reduce vacation time) or get a higher billable rate.
By planning on an annual cycle, you won't worry when your paycheck varies by $3,000 - $5,000 on a monthly basis. You'll know on average, it will be fairly predictable.
Want the full playbook? Check out Going 1099.