Happiness Has a Three-Month Memory

Think about the last time you got a raise.

The first paycheck felt great. You noticed the new number. Maybe you treated yourself to a nice dinner, or finally bought the thing you'd been eyeing.

A few months later, that same paycheck was just your paycheck.

The amount hadn't changed. You had.

The hedonic treadmill

In 1971, psychologists Philip Brickman and Donald Campbell gave this pattern a name: the hedonic treadmill.

When something good happens, we get a lift. Then, quietly, our expectations rise to meet the new situation, and the lift disappears. We keep moving toward more, but emotionally we end up roughly where we started.

It's not ingratitude. It's how people are built. The new phone stops feeling new. The bigger apartment becomes just "home." The raise becomes just "the salary."

In other words, the raise becomes the new baseline.

The experiment

So how long does the lift last?

In 1996, psychologists Eunkook Suh, Ed Diener and Frank Fujita set out to measure it. They followed 115 people for two years, tracking the good and bad events in their lives and how satisfied they felt.

The result was striking. Only events from the previous three months affected how people felt about their lives. Events older than that, good or bad, had faded into the background. They no longer showed up in people's happiness at all.

A promotion from last spring. A great vacation from last year. A frustrating setback from six months ago. By the time a season had passed, most of them had stopped moving the needle.

Happiness, it turns out, has a three-month memory. The raise doesn't expire. The feeling does.

Why more of the same doesn't fix it

If rewards fade, the obvious answer seems to be bigger rewards. But a bigger raise just resets a higher baseline. The treadmill speeds up.

What keeps people engaged isn't one big win. It's a steady sense of progress: something new to work toward, and proof that they're getting somewhere.

That's a design problem, not a willpower problem. And it's the problem MIMR is built to solve.

Where it gets complicated

The three-month finding is real, but it isn't a universal clock.

The Suh study was relatively small. And later, larger studies have found that some events last much longer. Losing a job or becoming disabled can affect well-being for years. Even income works more slowly than a single season: one large German study found that the happiness boost from higher income faded gradually over several years.

There's also the famous 1978 study of lottery winners, who weren't much happier than people who hadn't won. It's often cited as proof that good fortune fades. But a 2020 study of Swedish lottery winners found that large wins raised life satisfaction for years.

So the honest version is this: most everyday events lose much of their emotional punch within a few months, but not all, and not for everyone. Ninety days isn't a law of nature. It's a well-supported starting point.

Why 90 days works for more than happiness

The three-month window isn't the only reason MIMR runs on 90-day cycles. It also lines up with two other timelines.

It's long enough for your body to change. Many exercise studies find measurable gains in strength and fitness within about 8 to 12 weeks. A shorter cycle risks re-measuring before anything has had time to change.

It's long enough for a habit to form. In a 2010 study at University College London, new daily habits took a median of 66 days to become automatic, though the range was wide. Ninety days gives most people time to get past that point.

Long enough to change. Long enough to stick. Short enough that the reward still feels new.

How this shapes MIMR

Most reward programs are designed as if the treadmill didn't exist. You unlock a perk once, and it sits there forever. The goalposts never move. Engagement peaks early, then quietly fades.

MIMR works in 90-day cycles instead. Every cycle starts with a measurement and ends with measuring again. And each new cycle brings two things.

A new focus. Something fresh to work on, arriving before the last goal has gone stale.

A new reward. Timed to land right around when the glow from the last one would have worn off. And any reward money that isn't earned in one cycle rolls into the next, so nothing is lost.

Cycles are also more forgiving than streaks. Miss one day of a streak and the counter drops to zero, and for many people that's the moment they quit. A cycle has a natural beginning and end. If one season didn't go the way you hoped, the next one is a clean slate.

We'll be measuring whether 90 days is the right length, too. If engagement drops off at week eight, or people want more time, the data will tell us. That's the point.

A raise gives you one great season.

MIMR is designed to give you a new one every 90 days.

Measure · Improve · Measure · Reward