Mary-Jo, the IRS will look at the last 3 years of tax returns and either look for a trend or come up with an average income. So if the income is continuing to move up, they will use the current year. If it is trending down or up-and-down, then they will average the last 3 years. When they do this they may come up with a higher income than the current, but they dont increase the current taxes to match. So you always want to look at the last three years of tax returns and see what it looks like vs. the current.
If the IRS does want an average used instead of what you proposed, make sure they adjust the current taxes up to match the averaged income number.