CT-1120 GB: Green Building Tax Credit (2025)

Who files this form

Use the 2025 Form CT-1120GB to claim the Green Building Tax Credit against Connecticut Corporation Business Tax for eligible construction, renovation, or rehabilitation projects.

The credit is administered by the Department of Energy and Environmental Protection (DEEP). To qualify, an application must have been submitted to and approved by DEEP before December 1, 2017.

An eligible project is a real estate development project, or a building within one, designed to meet the applicable LEED Gold certification or an equivalent certification determined by DEEP.

When it's due

For the 2025 credit claim, the form lists these historical eligibility limits:

• The application must have been submitted to and approved by DEEP before December 1, 2017.
• Total credits claimed cannot exceed the amount of the tax credit voucher issued by DEEP before December 1, 2017.

The text does not give a filing due date for the 2025 form.

What you'll need

Have the following information available to complete the form:

• Corporation name and Connecticut Tax Registration Number.
• Beginning and ending dates of the income year.
• The 2020 Green Building Tax Credit amount from 2020 Form CT-1120GB, Part I, Line 5.
• Credit amounts applied during 2020 through 2024, the carryforward to 2025, and the amount applied to 2025.
• For members included in a 2025 Form CT-1120CU combined return, credits shared with and used by another combined-group member.

The form also limits total credits claimed to the amount of the DEEP tax credit voucher.

How to file

Complete the form in blue or black ink only. Do not use staples, and use the correct year's form.

1. Enter the corporation name, Connecticut Tax Registration Number, and income-year dates.
2. On Line 1, Columns A through D, enter the corresponding credit and carryforward amounts.
3. On Line 2, Column D, enter the total credit applied to 2025.
4. If you are a member included in the 2025 Form CT-1120CU, include in Column D credits shared with and used by another combined-group member.

No carryforward to 2026 is available. The supplied text does not provide a mailing address or e-filing instructions.

Common mistakes

• Using the wrong year's form. Each form is year specific, and the correct year's form must be used.
• Using other ink or staples. Use blue or black ink only, and do not staple the form.
• Carrying a balance to 2026. The 2025 computation instructions expressly state that no carryforward to 2026 is available.
• Carrying the credit back. No carryback is allowed.
• Including excluded costs. Land purchases, remediation costs, telephone systems, and computers are not allowable costs.
• Exceeding the voucher amount. Total credits claimed cannot exceed the amount of the DEEP tax credit voucher issued before December 1, 2017.

Questions people ask

Can the credit be transferred?

Yes. The credit may be assigned to another taxpayer or taxpayers. A project owner, including a nonprofit entity, may transfer a credit to a pass-through partner in return for a lump-sum cash payment.

How is the credit calculated?

The credit equals allowable costs multiplied by the applicable credit percentage. The form says a taxpayer may claim only 25% of the total allowable costs in any year. For new construction or major renovation, the rates are 8% for LEED Gold and 10.5% for Platinum. For core and shell or commercial interior projects, the rates are 5% for Gold and 7% for Platinum.

Can an unused credit be carried forward?

The general rule allows unused credit to be carried forward for up to five income years, with no carryback. However, the 2025 form specifically states that no carryforward to 2026 is available.

Where can I find more information?

The form directs taxpayers to the Guide to Connecticut Business Tax Credits on the Department of Revenue Services website at portal.ct.gov/DRS.

Official sources

• https://portal.ct.gov/-/media/drs/forms/2025/corp/ct-1120gb_1225.pdf