Material Assistance Cost Ratio (MACR): The 40% Threshold Commercial Buyers Must Hit in 2026

If your Colorado business is planning a commercial solar project that begins construction in 2026, the material assistance cost ratio is a number you cannot afford to ignore. In short: a qualified solar facility that begins construction during 2026 must keep its material assistance from prohibited foreign entities below the threshold set by federal rules, and for projects starting in 2026 that threshold sits at 40%. Clear that bar and your project stays eligible for the Section 48E investment tax credit. Miss it and the credit can be denied entirely. This guide explains what the ratio measures, where the 40% figure comes from, and the practical steps to stay on the right side of it.

A note before we go further. This is a fast-moving area of tax law. The rules trace to the One Big Beautiful Bill Act (OBBBA) and to IRS interim guidance issued in Notice 2026-15, released February 12, 2026. Treasury is required to publish formal safe-harbor tables for this calculation by December 31, 2026, which means the mechanics described here can and likely will change. Treat the figures below as the current state of play as of mid-2026, and confirm specifics with a qualified tax advisor before you commit.

What the Material Assistance Cost Ratio Measures

The material assistance cost ratio, sometimes shortened to MACR, is a sourcing test. It exists to enforce the new Prohibited Foreign Entity (FEOC) restrictions that OBBBA layered on top of the clean energy credits. The idea is simple even if the arithmetic is not: Congress wants federal solar incentives to flow to projects that are not too dependent on materials and components made by certain foreign adversary entities.

To do that, the rules ask you to look at the manufactured products and components that go into your solar facility and figure out how much of their cost comes from prohibited foreign sources versus everything else. The ratio compares the cost attributable to prohibited foreign material assistance against the total relevant cost of the manufactured products in the project. If the share tied to prohibited sources is too high, the project fails the test.

The material assistance cost ratio is closely related to, but separate from, the broader set of FEOC compliance rules. The FEOC framework governs who can own, control, and supply a project. The cost ratio is the specific quantitative gate that determines whether your supply chain passes. For a fuller picture of ownership and control restrictions, see our overview of FEOC solar compliance, which this post builds on.

Where the 40% Threshold Comes From

The 40% figure is a year-keyed threshold. Under OBBBA and the FEOC guidance, qualified solar and wind facilities that begin construction in 2026 must hold the cost share attributable to prohibited foreign material assistance under 40% of the total. Put another way, at least 60% of the relevant manufactured-product cost must come from sources that are not prohibited foreign entities.

The threshold is not static across years. It is designed to tighten over time, ratcheting the required non-prohibited share upward for projects that begin construction in later years. That is one reason the begin-construction date matters so much, and why many Colorado businesses are working to lock in a 2026 start. The earlier your begin-construction year, the more forgiving the sourcing threshold tends to be.

Because the rule is tied to the begin-construction date, the safe-harbor and physical-work timing decisions you make for the broader credit interact directly with the cost ratio. If you are still mapping out the credit itself, start with our explainer on the Section 48E tax credit for commercial solar, then layer the sourcing analysis on top.

How the Calculation Works in Practice

At a high level, the material assistance cost ratio is computed for the manufactured products and manufactured-product components that make up your facility. The calculation generally follows these steps:

1. Identify the manufactured products in the project: modules, inverters, racking, and other listed components.
2. Determine the total relevant cost of those manufactured products.
3. Determine how much of that cost is attributable to material assistance from prohibited foreign entities.
4. Divide the prohibited-source cost by the total relevant cost to get the ratio.
5. Compare the result against the year-keyed threshold, which is 40% for a 2026 begin-construction date.

The wrinkle is in step three. Pinning down exactly how much of a component cost is attributable to prohibited foreign material assistance is genuinely difficult, especially with global supply chains where a single inverter or module passes through several countries. That is precisely why Treasury is on the hook to publish safe-harbor cost tables by December 31, 2026. Those tables are expected to assign default cost percentages to common components and source countries so buyers do not have to trace every bolt and cell. Until those tables land, Notice 2026-15 provides interim rules, and many projects are relying on supplier documentation and manufacturer certifications.

Why Supplier Documentation Matters

Because the ratio depends on cost attribution, the paperwork from your equipment suppliers becomes the backbone of compliance. Practically, that means collecting and retaining:

• Manufacturer certifications stating the origin and cost breakdown of modules, inverters, and racking.
• Bills of materials that map component costs to their sources.
• Documentation that supports any safe-harbor percentages you rely on once the Treasury tables are final.
• Records tied to your begin-construction date so the correct year threshold applies.

This is record-keeping you want to start now, not reconstruct at audit. A clean paper trail at the time of purchase is far easier than chasing certifications a year later. Suppliers who sell into the U.S. commercial market are increasingly prepared to furnish this documentation, but quality varies. A vendor who shrugs at an origin-and-cost certification request is a vendor who can quietly put your credit at risk, and that is worth weighing against any per-watt savings they offer.

The Interim-Guidance Reality

It is worth being honest about how unsettled this corner of the law is. Notice 2026-15 is labeled interim guidance for a reason: it gives taxpayers a workable framework while Treasury finishes the detailed rules. Between now and the December 31, 2026 deadline for the safe-harbor tables, expect clarifications, possible corrections, and additional examples. Some projects beginning construction in the second half of 2026 may find the tables published before they finalize procurement, which would simplify their analysis considerably. Others that start earlier may need to rely on supplier data and reasonable, well-documented methods. Neither path is wrong, but each calls for a tax advisor who is tracking the guidance as it evolves rather than working from a single snapshot in time.

How MACR Relates to the Domestic Content Bonus

It is easy to confuse the material assistance cost ratio with the domestic content bonus, because both look at where your equipment comes from. They are different tests with different goals, and a project can be subject to both.

• The material assistance cost ratio is a gate. It is a pass-or-fail requirement that protects your base Section 48E credit. Fail it and you can lose the credit.
• The domestic content bonus is an adder. It is an optional sweetener that adds 10 percentage points to your credit if you hit a domestic-sourcing threshold.

In practice, the sourcing strategy that helps you clear the material assistance cost ratio often helps you toward the domestic content bonus as well, because both reward moving away from prohibited foreign supply chains and toward domestic or allied production. The thresholds and definitions differ, though, so you cannot assume that satisfying one automatically satisfies the other. If you want to capture the extra 10 points on top of clearing the FEOC gate, read our guide to the domestic content bonus for solar and plan both into your procurement decisions from the start.

What This Means for Colorado Commercial Buyers

For a business owner along the Front Range or on the Western Slope, the practical takeaway is straightforward. If you intend to claim the Section 48E credit on a project beginning construction in 2026, your equipment sourcing is now a tax-eligibility decision, not just a price decision. The cheapest panel on a spreadsheet may carry a sourcing profile that pushes you over the 40% threshold and jeopardizes a credit worth far more than the equipment savings.

This is where working with an installer who understands both the engineering and the federal rules pays off. At ProGreen Solar, we build commercial systems across Colorado and as a licensed electrical contractor (EC.0101788) we coordinate the equipment selection, documentation, and construction-start timing that these credits hinge on. We cannot give you tax advice, and we will always tell you to confirm the numbers with your CPA. What we can do is help structure the project and the procurement so your tax team has clean, defensible records to work with.

Consider a simplified example. Suppose a warehouse owner in Longmont is comparing two module suppliers for a 2026 project. Supplier A is a few cents per watt cheaper, but cannot document the origin and cost breakdown of its cells and modules, and its supply chain leans heavily on prohibited foreign sources. Supplier B costs slightly more but provides full certifications and sources from facilities outside the prohibited set. On a pure equipment-price comparison, Supplier A looks better. But if Supplier A pushes the project's prohibited-source cost share toward or past 40%, the owner risks the entire Section 48E credit, which on a commercial array is typically worth far more than the modest equipment premium Supplier B charges. When you frame it that way, the higher-documented option is usually the cheaper option once the tax math is included. This is the kind of tradeoff that should be evaluated before the purchase order is signed, not discovered at tax time.

A few moves worth making now:

• Lock in your begin-construction year deliberately, since the threshold is keyed to it.
• Vet equipment vendors on their willingness to provide origin and cost certifications, not just price.
• Keep your tax advisor in the loop early so the structure matches the latest interim guidance.
• Plan for the Treasury safe-harbor tables, which should simplify the math once published by the end of 2026.

The Bottom Line on the 40% Threshold

The material assistance cost ratio turns supply-chain sourcing into a federal tax-credit requirement. For commercial solar projects beginning construction in 2026, the prohibited foreign material assistance share must stay under 40% to protect the Section 48E credit. The rules sit on interim guidance in Notice 2026-15 for now, with formal Treasury safe-harbor tables required by December 31, 2026, so expect refinements and confirm the current state with your advisors before you commit.

If you are weighing a commercial solar project in Colorado and want help sequencing the begin-construction timing, sourcing the right equipment, and keeping the documentation a credit claim demands, our team is ready to walk the project with you. Learn more about our commercial solar work and let us help you build a system that pencils out on both the energy and the tax side.

Frequently Asked Questions