Guess, then see: why tasks take longer than you think

Why tasks take longer than you think

You sit down to a task you’re sure will take 20 minutes. An hour later you’re still on it. The next morning you plan the day the same way.

This has a name: the planning fallacy. It’s a well-studied mistake in how people plan, and it happens to most of us, with or without ADHD.

What the research found

In a 1994 paper, Buehler, Griffin and Ross asked university students when they expected to finish their honours thesis. On average they guessed about 34 days. It took about 55. Across the paper’s studies, people guessed too short for their own tasks, from schoolwork to everyday jobs. When people thought out loud while guessing, they talked mostly about how this time would go, not how similar tasks had gone before. In one study, remembering past tasks wasn’t enough on its own. When people were also asked to link those memories to the task in front of them, the bias went away.

A 2005 review by Roy, Christenfeld and McKenzie argues for a second reason: our memory of how long past tasks took tends to run short. If so, a guess built from memory starts out too small, however honest it is.

That points to a fix. In a 2008 paper, Roy, Mitten and Christenfeld told people how long a similar task had really taken before they guessed. In three experiments, with university students and with members of the public at places like fast-food restaurants, the guesses got more accurate. People predicted better from measured time than from memory. These were single tasks, so they don’t show that weeks of checking change your sense of time. You don’t need that, though: the number does the work. None of these planning studies looked at ADHD.

What about ADHD?

Some people with ADHD call this time blindness. The research is less tidy than the name. A 2022 meta-analysis by Marx and colleagues pooled 55 lab studies, where people judge or copy short spans of time, often seconds long. On average, people with ADHD were less accurate and their judgements varied more. But seconds in a lab aren’t an afternoon of homework. For adults, a 2023 review by Mette found very few studies and mixed results.

A small 2011 study by Prevatt and colleagues came closer to real work. It compared 20 college students with ADHD and 20 without on a task like schoolwork. The groups differed on several measures. The authors pointed to one weak spot: judging afterwards how long the task had taken. That’s the kind of memory a guess is built from.

So most of us guess short. Lab timing tasks are harder with ADHD on average, though how much that stretches task guesses hasn’t been well tested. Either way, the fix doesn’t rely on willpower. It relies on a record.

Try this week

Pick three tasks you’ll do this week anyway: a reading, an email, the dishes. Before each one, think of something similar you’ve done and what it really took. Then write your guess in minutes on a sticky note. Time it, and write the real time beside it. The gap is information, not a grade. If the week only fits one task, that’s fine too.

Guess, then see

You’ll need to be signed in and using the Full layout. A few runs in, the timer offers this once: press Try it. Or turn it on any time under Settings → What’s on screen → Guess, then see.

1. Name the task in What are you working on?, or tap one of your most-used tasks under the box.
2. Guess how long it will take: appears, with 15m, 30m, 45m, 1h and 2h. Tap one before you press Start focus: only runs that start after the guess count.
3. Work in as many runs as it needs, with the same name each time. Runs are matched by the name exactly as typed. Only time in runs counts, not breaks. The real time is never typed in or remembered: it’s what the timer measured.
4. When it’s finished and no run is going, press Done with this task (or Done in Your guesses). You’ll see something like ‘You guessed 30m. It took 52m.’
5. After three finished tasks, Your guesses, below This week, shows your pattern, such as ‘Lately your tasks take about 1.6× your guess’. It uses the middle of your last 10, so one odd task can’t swing it.

For a to-do in My Day, type its name in the box exactly as it reads in your list, then guess. Then start it as usual: press Start on its row, or pick it above Start focus. Ticking the to-do doesn’t close the guess, so press Done with this task too.

A pattern of 1.6× means a task you’d guess at 30 minutes has tended to take about 50. That isn’t a score. It’s a planning number, and when tasks run long the timer suggests using it for your next guess. Plans change: Forget in Your guesses clears an open guess that no longer fits, and it isn’t counted. Guesses are private and never shown to a group.

You know your own tasks best

It feels true. Yet in the 1994 paper, people underestimated how long their own tasks would take, but not other people’s. Inside a task, the plan fills your head. The past, written down, is the view from outside.