I find three of the most common “do-it-yourself” tax preparation mistakes include capital gains, business asset depreciation and rental home cost basis.
Many people do not know the difference between short-term (1 year or less) and long-term (1 year and 1 day+) capital gains tax treatment. I have met individuals who had to pay more in tax then necessary because they sold their asset within a day or two of it becoming a long-term asset. Knowing the difference between short-term and long-term capital gains can save you up to 20% or more on your federal return. If you receive an inherited asset, it is deemed to be a long-term capital gain and it receives a step-up in basis. This means your basis is what it was worth on the day the grantor died. If you have capital gains on your return and/ or your received an inherited asset, I strongly encourage you to seek out a professional and competent tax professional.
Moreover, another area worth significant tax savings on your return is calculating and planning your business asset deprecation correctly. I have had to amend many returns to correct their depreciation schedules. It is important you keep your purchase documentation for business assets and allow your tax professional to determine the best course of action in preparing your depreciation schedules. Many times, if I have a start-up business, it is more advantageous to depreciate business assets rather than taking a Section 179 expense deduction. If your business is showing a loss even before you have calculated depreciation, it is probably not in your best interest to expense the asset.
Finally, cost basis tracking on rental properties is another area where I see common mistakes. This is especially evident with converted personal to rental property. If you convert your home from a personal residence to a rental, your basis for depreciation is either the FMV (Fair Market Value) or adjusted basis at the time the property was converted. The adjusted basis is the original purchase price of the home in addition to many improvements and purchasing expenses. The basis for your rental property is the lower of these numbers (current FMV or adjusted cost basis).
Unless you have a very simple tax return, I strongly encourage you to seek out the advice of a competent professional. Tax preparation work is very tricky and can cost you in the long run if it is not done correctly. If you have capital gains, business depreciation or rental property on your return, I would consult with either a CPA or Enrolled Agent before filing your own return. The value of a good professional should far outweigh any fee they may charge.