OK ... on the new car you get the choice :
1) use the standard mileage rate ... if you choose this option in the first tax year you can "flip flop" between these 2 options
2) choose the actual expenses option + depreciation ... if you choose this option you MUST use this option for the entire life of this vehicle
FYI ... depreciation starts with the total cost of the vehicle ... the down payment or other payments is immaterial.
Finance costs are deductible either way on the Sch C.
If you are new to being self employed, are not incorporated or in a partnership and are acting as your own bookkeeper and tax preparer you need to get educated ....
If you have net self employment income of $400 or more you have to file a schedule C in your personal 1040 return for self employment business income. You may get a 1099-Misc for some of your income but you need to report all your income. So you need to keep your own good records. Here is some reading material……
IRS information on Self Employment….
http://www.irs.gov/Businesses/Small-Businesses-&-Self-Employed/Self-Employed-Individuals-Tax-Center
Publication 334, Tax Guide for Small Business
http://www.irs.gov/pub/irs-pdf/p334.pdf
Publication 535 Business Expenses
http://www.irs.gov/pub/irs-pdf/p535.pdf
Home Office Expenses … Business Use of the Home
https://www.irs.gov/businesses/small-businesses-self-employed/home-office-deduction
https://www.irs.gov/pub/irs-pdf/p587.pdf
Publication 946 … Depreciation
https://www.irs.gov/pub/irs-pdf/p946.pdf
