Model dividends in After-Tax Growth assumptions on My Plan > Savings and Assets.
Include dividend growth in the real growth assumptions for each account. This assumes that dividend growth will be reinvested and added to the cost basis. For example, if you anticipate the account will grow at 5% and yield 1% of dividends, enter a growth assumption of 6%.
Then, add the same percentage of dividend growth to the "Turnover" rate. The "Turnover" rate will determine the percentage of the account to realize as long term gains on an annual basis. If you are invested in index funds or ETFs, your "Turnover" percentage will be very low. If you are invested in mutual funds or are an active investor, your "Turnover" percentage may be higher. Add the dividend growth rate to the "Turnover" percentage. This will model a long term gains tax liability rate for dividends each year.
Building on the example above If you assume a 2% "Turnover" rate without dividends and modeled 1% of divided growth, enter 3% as the turnover rate.