How to find out whether I am under accrual or cash basis on my 1120S tax return?

If you do not know what accounting method is used for your taxes, you should consult the person who files your tax returns on your behalf as the selected accounting method is the one that has been used for all other tax returns unless you requested to change that method by filing a form for that request with the IRS.

See Schedule B, Line 1 which asks youto identify your accounting method. However, from time to time, the answer does not reflect the reality. So, have an experienced tax professional take a look at your return. Obviously, asking the preparer, as the previous attorney suggested, is the first person I would ask.