What is a material adverse change?
A material adverse change — often called a MAC, or material adverse effect (MAE) — is a contractual provision that allows a buyer to refuse to close, or to renegotiate, if the target business suffers a serious and durable deterioration between the signing of the agreement and the closing date. It is the principal mechanism that allocates the risk of something going badly wrong with the business in the gap between signing and close.
The clause typically appears as a closing condition and as a qualifier woven through the seller's representations and warranties. If a MAC has occurred, the buyer's obligation to complete the purchase falls away, giving it leverage to walk or to push for a price reduction.
What actually counts as "material" is the hardest-fought language in many agreements. Courts in major deal jurisdictions have historically set a very high bar — the change generally must be substantial and durationally significant, not a short-term blip or a cyclical downturn the parties should have anticipated.
How a MAC clause actually works
The clause is structured around a general standard and a set of negotiated exceptions.
- The general standard. A change, event, or effect that is materially adverse to the business, results of operations, or financial condition of the target.
- Carve-outs. Exclusions that do not count as a MAC — typically general economic or industry-wide conditions, changes in law or accounting rules, and effects of the deal's announcement. The buyer takes systemic risk; the seller is protected from broad market moves.
- Disproportionate-impact exception. A carve-out is often itself qualified: an industry-wide event can still count as a MAC if it hits the target disproportionately compared with peers.
- Forward-looking language. Many clauses cover effects that "would reasonably be expected to" have a material adverse impact, not only effects already realized.
The net effect of this layering is that the buyer bears general market risk while the seller bears risk specific to its own business — and proving a MAC has occurred is notoriously difficult.
Why MACs are so hard to invoke
In practice, successfully calling a MAC to exit a deal is rare. The bar set by courts in leading jurisdictions is deliberately high: a buyer must usually show a decline that is both substantial in magnitude and durationally significant — a change that fundamentally and lastingly alters the earnings power of the business, not a temporary shock.
The clause is therefore as much a negotiating lever as a literal exit. The credible threat of invoking a MAC — even when the legal case is uncertain — often pulls the parties back to the table to renegotiate price or terms rather than litigate. The carve-outs determine who carries which risk, and the litigation record around them is what gives the words their real meaning.