What is tentative minimum tax (TMT)?

TMT is the tax calculated under the AMT system before subtracting the AMT foreign tax credit. It serves as a floor for the GBC limitation to prevent business credits from reducing tax below the AMT level.

Can the R&D credit be applied against payroll tax?

Yes. Qualified small businesses (under $5 million in gross receipts, with less than 5 years of gross receipts) can elect to apply up to $500,000 of the R&D credit against payroll taxes instead of income taxes.

Tax Credits (FTC, GBC)

How the General Business Credit Works: Form 3800 Mechanics

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Key Takeaways

Calculate each credit separately, then combine on Form 3800
GBC limitation = net tax minus greater of TMT or 25% of net tax above $25,000
Allowable credit is the lesser of total credits or the limitation
Excess carries back 1 year or forward 20 years
Oldest credits are applied first (FIFO order)

GBC Calculation Process

To calculate your General Business Credit, start by computing each individual credit on its respective form (e.g., Form 6765 for R&D, Form 3468 for energy). Bring each credit amount to Form 3800 and add them together to get your total current-year GBC.

Next, determine your GBC limitation: net income tax minus the greater of your tentative minimum tax or 25% of net regular tax above $25,000. The allowable GBC for the year is the lesser of your total credits or the limitation amount.

Carryback and Carryforward

If your total credits exceed the limitation, the excess is not wasted. You can carry the excess back 1 year (amending the prior year's return) or carry it forward up to 20 years. This flexibility ensures that business credits provide long-term value even in years when your tax liability is insufficient to absorb them all.

Credits are applied in chronological order — oldest carryforwards are used first, then current-year credits, then carrybacks.

tax creditsforeign tax creditgeneral business creditform 3800