Utilize your financial knowledge, give your answer or opinion to the input question or subject . Answer format is not limited.

Reducing taxable income in US in December
Assuming that what you want to do is to counter the capital gains tax on the short term and long term gains, and that doing so will avoid any underpayment penalties, it is relatively simple to do so. Figure out the tax on the capital gains by determining your tax bracket. Lets say 25% short term and 15% long term or (0.25x7K) + (0.15*8K) or $2950.  If you donate to charities an additional amount of items or money to cover that tax. So taking the numbers in step 1 divide by the marginal tax rate $2950/0.25 or $11,800.  Money is easier to donate because you will be contributing enough value that the IRS may ask for proof of the value, and that proof needs to be gathered either before the donation is given or at the time the donation is given. Also don't wait until December 31st, if you miss the deadline and the donation is counted for next year, the purpose will have been missed. Now if the goal is just to avoid the underpayment penalty, you have two other options.  The safe harbor is the easiest of the two to determine. Look at last years tax form. Look for the amount of tax you paid last year. Not what was withheld, but what you actually paid. If all your withholding this year, is greater than 110% of the total tax from last year, you have reached the safe harbor. There are a few more twists depending on AGI Special rules for farmers, fishermen, and higher income taxpayers.   If at least two-thirds of your gross income for tax year 2014 or 2015   is from farming or fishing, substitute 662/3% for 90% in (2a) under   the General rule, earlier. If your AGI for 2014 was more than $150,000   ($75,000 if your filing status for 2015 is married filing a separate   return), substitute 110% for 100% in (2b) under General rule ,   earlier. See Figure 4-A and Publication 505, chapter 2 for more   information.