One in, one out

One in, one out is the oldest decluttering rule there is. For each new thing that comes into your home, one thing of the same kind goes. The count in each drawer stays where it is, and every purchase becomes a trade instead of an addition.

It is easy to start and easy to get subtly wrong. Run carelessly, it can even speed up the very chain it is supposed to stop. This page covers how to run it so it holds.

Why it works

The rule puts a price on every purchase that is not money: you have to give something up. That price is felt. In the classic experiments by Daniel Kahneman, Jack Knetsch and Richard Thaler, people who had just been handed a coffee mug asked for more than twice as much to sell it as other people would pay to buy one. That is the endowment effect, and it is usually a seller’s friend. Here it works for you. Having to name the mug that leaves makes the new mug cost more than its price tag, and that small sting is often enough to end the purchase. It is the same sting that drives loss aversion, turned into friction.

It also sets a hard limit. Mental budgets, as Chip Heath and Jack Soll described them, hold best when the category has a fixed size. Here the size is the shelf.

How it stops a chain at the door

Grant McCracken, who named the Diderot effect, described how the things we own form sets that seem to belong together. A new item that outclasses the set makes the rest look wrong, and replacing them one by one is how a chain runs.

One in, one out can block that, or feed it. It blocks it when you choose what leaves before you buy, because you are deciding from the whole category. It feeds it when the thing that leaves is always the one the new purchase made look shabby: the new rug arrives, the old rug looks sad, so the old rug goes, and the room is one link further along. The seven rules for avoiding the effect flag the same risk. The fix is in step 2 below.

The steps

1. Define your categories by storage. A category is whatever shares a drawer, shelf, rail or cupboard: coats, mugs, the bookshelf, kitchen gadgets. Decision rule: if two things are stored together, they are one category.
2. Name the outgoing item before you buy. Pick it from the least-used end of the category, such as the shirt you have not worn this year or the pan you never reach for. Do not pick the item that sits next to the new one. Decision rule: if you cannot name an outgoing item you would be glad to see go, there is no room, and you do not buy.
3. Swap like for like. A coat for a coat, a mug for a mug. A set counts in full: six new glasses mean six glasses leave.
4. Get it out within seven days. Keep a box by the door. Donate, sell, give away or recycle. Decision rule: whatever is still in the box on day seven goes to donation that day.
5. Write it down for a month. Note each swap, in and out. You will soon see which categories are under pressure.

Where the rule fails

Consumables. Shampoo, coffee, printer paper and batteries are used up, not kept. Counting them is meaningless, and “one in, one out” with a bottle of soap is just shopping. Use a stock limit instead: one open, one spare, and the spare is bought only when the open one runs out.

Tools and equipment. A drill does not replace anything, and a count would push you either to keep a bad tool or to refuse a needed one. Judge tools by job, not number. Decision rule: one tool per job. If a new tool does a job an old tool already does, the old one leaves. If the job is new, buy only if you will do it at least a few times a year; otherwise borrow or rent.

Growing children. Outgrown clothes and shoes are replacements, not swaps. Their rule is size, not count. Toys and books are a different story, and they suit the stricter version below.

One in, two out: the ratchet

When a category has grown past what you want, one for one only holds it there. To bring it down, run one in, two out: each new item sends two of its kind away. It is slow, which is the point. Every purchase now shrinks the category, and you get choosier about what comes in.

Set a target before you start, such as 30 tops or two shelves of books (illustrative numbers), and switch back to one for one once you reach it. A ratchet with no finish line becomes a chore, and chores get dropped. For a faster result, pair it with a one-time edit of the category, then use one in, one out to hold the new size.

Variations

• Small apartments. Use space instead of count: the shelf is full, so something comes off before anything goes on.
• Shared homes. Each person runs the rule for their own categories. Shared categories, such as the kitchen or the living room, need both people to agree on the outgoing item.
• During a no-buy or low-buy year. The rule governs the categories with caps in a low-buy year, and the outgoing item still has to leave within the week.
• Furniture. One room at a time works better than item by item, because rooms are where chains form. See one room at a time.

What goes wrong, and the fix

• The “out” never leaves. It sits in a bag in the closet for months. Fix: the seven-day box.
• Every swap is an upgrade. The cheap pan goes, a better pan comes, then a better knife to match. Researchers have found that when an appealing upgrade is in view, people start treating what they own carelessly, and a working item slides toward “worn out.” Fix: the outgoing item must be the least-used one, not the most worn, and the incoming one should be at the level of the rest of the set. A personal uniform makes this easier for clothes.
• Hoarding trade tokens. You keep things you never use so that you have something to give up next time. Fix: once a year, edit each category on its own, with no purchase attached.
• Category drift. A new bag “replaces” a scarf. Fix: storage defines the category. If it lives somewhere else, it is not a swap.