Across seven studies with 2,311 people, negotiators who made a series of shrinking concessions tricked the other side into believing they had hit their limit. The other side then made less ambitious counteroffers and settled for worse deals (Tey, Schaerer, Madan & Swaab, 2021). The Ackerman Model is a bargaining formula built entirely around exploiting that.
A concession that shrinks each time is a message: “I’m almost out of room.” Your counterpart hears it, believes it, and stops pushing.
The formula
It is a precise FBI haggling script (from Mike Ackerman, popularized by Chris Voss). Say your target, what you actually want to pay, is $1,000.
| Step | Offer | % of target | The jump |
|---|---|---|---|
| 1 | $650 | 65% | the opening anchor |
| 2 | $850 | 85% | +20% |
| 3 | $950 | 95% | +10% |
| 4 | $1,037 | ~100% | +5% |
And the rules around the numbers:
- Open at 65% of target. An aggressive anchor that drags their whole frame down.
- Raise in halving increments: +20, then +10, then +5. Each concession is half the last.
- Make them counter before each raise. Use calibrated questions and “no” so you never bid against yourself.
- Make the final number precise and odd, not $1,000 but $1,037.
- Throw in a small non-monetary extra at the very end.
Why each piece works
Every step in the script is quietly doing a job:
- The 65% open is an anchor, extreme but not insane. It shocks their reference point downward before bargaining even starts.
- The halving increments are the genius. +20 → +10 → +5, each raise half the last, so the pattern screams “I’m running out of room.” They conclude it and stop pushing.
- Countering before each raise keeps every raise looking hard-won, and saves you from the blunder of bidding against yourself.
- The precise final number ($1,037, not $1,000) reads as a calculated bottom, not a round guess that invites one more push.
- The non-monetary throw-in (“…and I’ll throw in my old monitor”) makes them feel they squeezed out every last dollar.
The real magic is the second one. The shrinking pattern does the persuading, exactly as Tey et al. found:
The model never says “this is my limit.” It makes the other person conclude it, which they believe far more than anything you could claim.
The defense
The same study found one thing that protects you from shrinking concessions: keep your eyes on your own target.
When someone runs this on you, do not read their tiny last step as proof they are tapped out. That is the illusion. Anchor to what the thing is actually worth and what you came to get, not to the shape of their offers.
Why this matters
- It is a script, so it removes emotion. You execute a plan instead of reacting.
- The pattern of your offers speaks louder than any “final offer.”
- Precision and a throw-in close the gap between almost and done.
- The counter is a target. Hold your own number and the shrinking-concession illusion loses its grip.
Concede in halves, land on an odd number, and give away something tiny at the end. By then they are not taking your money. They are winning it.