Don’t let penalties for underpaid taxes increase your tax bill next April. Check the total you’ve paid in for 2015 through withholding and/or estimated taxes. If you’ve underpaid, consider adjusting your withholding for the final months of the year or increasing your remaining quarterly estimate. If you employ household workers, be sure your calculations include the payroll taxes you’ll owe for them. Remember to include the 3.8% tax on net investment income in your planning too.