You wrote: Unless you are filing as a farmer, who have special rules for estimated tax payments, you can ignore line 14 code C.
First, 14C doesn't have to do with Estimated Tax Payments; the method is used to figure your net earnings from self-employment for calculation of self-employment tax. Further, you don't need to be a farmer to apply the alternate method of calculating self employment tax.
IRS Instructions say:
You may be able to use this method to figure your net earnings from nonfarm self-employment if your net nonfarm profits were less than $6,107 and also less than 72.189% of your gross nonfarm income. Then the instructions go on to give you the calculation method.
