Most people can just estimate their income. It's based on an estimate anyway, so just go with your best guess.
To do that:
1. Other Tax Situations.
2. Select Start or Update by Form W-4 and estimated taxes.
3. Choose Yes to Adjust How Much Tax You Pay.
4. Walk through the next screens to enter your anticipated 2017 income. When you successfully complete all the questions, you can print out a new W-4 to give to your HR department at work.