Carryback and Carryforward Rules for Purchased Tax Credits

If you buy more credit than you can use, the unused part is not automatically lost. The rules differ by credit type and by whether you are an individual subject to §469.

The general rule (§39(a))

Unused general business credit is generally carried back one year and forward 20 years. The statute sends the entire unused credit to the earliest of the 21 years to which it may be carried, and any remainder to the other 20 years.

Applicable credits: 3 back, 22 forward (§39(a)(4))

For an "applicable credit" as defined in §6417(b), §39 applies separately, the carryback is three taxable years, and the carryforward is 22 taxable years. The §6417(b) list includes the §45, §45Q, §45U, §45V, §45X, §45Y, §45Z, §48, §48C and §48E credits and a portion of §30C. Check whether your credit is on the list.

Carryback specifics

§39(b) limits the amount that can be carried back to a prior year. If the buyer had no tax in a prior year or the room was already used, a carryback does not help. Carrying back also raises refund-claim and timing issues for your CPA.

Passive activity credits for individuals

A credit disallowed under §469 is carried forward to the next year and can be used when passive income tax arises. Confirm with your CPA how a purchased credit disallowed under §469 is tracked on Form 8582-CR and how the §6418 regulations treat unused amounts for the transferee (§1.6418-5).

Why carryover is a backup, not a plan

• Money paid today for credit used years later earns a lower effective return.
• Carryforward use is still subject to §38(c) each year.
• Purchased credit cannot be transferred again (§6418(e)(2)).
• Accounting realizability may be questioned (ASC 740).

Example: buying more than this year's room

A company can use $300,000 of credit this year but buys $500,000. The $200,000 remainder carries forward. If it is used two years later, the cash paid for it has been outstanding two years before the benefit arrives. At a 92 cent price, paying $184,000 for credit used in year three produces a smaller annualized return than paying $276,000 for credit used now.

Credit class	Carryback	Carryforward
General business credit (default)	1 year	20 years
Applicable credit (§6417(b))	3 years	22 years

Checklist

1. Confirm whether your credit is an applicable credit under §6417(b).
2. Model use year by year against §38(c).
3. For individuals, model §469 first.
4. Decide the purchase size so that carryover is a margin of safety, not the plan.

Educational only. We read §39 and §6417(b) as published on Cornell LII; verify against the current Code.