How to Say I Forgot in Japanese: Wasureta, Wasurechatta and Omoidasenai

Wasureta and wasuremashita: the basic forms

Wasureru, 忘れる, is a regular ichidan verb, so its forms are easy to build. The plain past wasureta is what you say to friends and family, and the polite past wasuremashita is the safe default with shop staff, teachers, colleagues and anyone you have just met.

The thing you forgot is marked with o. In speech the o is often dropped between friends, so saifu wasureta and saifu o wasureta both sound natural. With people you speak politely to, keep the particle.

Adding regret: wasurete shimatta and wasurechatta

On its own, wasureta can sound like a flat report. When you feel bad about forgetting, Japanese speakers usually add shimau, which carries the sense of something unfortunate that cannot be undone. In casual speech wasurete shimatta shrinks to wasurechatta, one of the most common things you will hear when someone pats their pockets at a station gate.

At work or with anyone you owe an apology to, use wasurete shimaimashita and follow it with sumimasen or mōshiwake arimasen. The shimau part does a lot of the apologising for you, because it shows that you regret what happened.

Ukkari means carelessly or without thinking and pairs naturally with forgetting. Sukkari means completely. Both help your apology sound sincere rather than mechanical.

Wasureta or wasureteta: forgot versus had forgotten

Learners often miss the difference between wasureta and wasurete ita, usually shortened to wasureteta in speech. Wasureta reports that forgetting happened. Wasureteta describes a state: it had slipped your mind, and you have only just realised. When a friend reminds you about their birthday dinner tonight, a natural reaction is a, wasureteta, not wasureta.

The same logic applies to politeness. Wasurete imashita is the polite form of had forgotten, and it sounds softer and more natural than wasuremashita when someone has just reminded you of something.

Forgetting an item: wasureru versus okiwasureru

When you forget to bring something, wasureru is enough. When you left something behind in a particular place, Japanese prefers okiwasureru, literally to put down and forget. That verb uses ni for the place, so you leave an umbrella ni the train, not de.

Lost property is called wasuremono, forgotten things, and it is a word you will see at stations, hotels and schools. Staff at a lost-property counter will usually ask when, where and what the item looks like, so have those three pieces ready. For a wallet or phone that may have been lost rather than left behind, the verb changes to nakusu or otosu, to lose or drop.

Forgetting a name without offending anyone

Forgetting someone's name happens to everyone, but saying o-namae o wasuremashita straight out can make the other person feel unimportant. The kindest approach is often to ask again without using the word forget at all, prefaced with a softener such as shitsurei desu ga, excuse me but.

If you do want to own it, add regret and a softening phrase. In business settings you may hear the formal verb shitsunen suru, to lose from memory, which sounds more measured than wasureru. A phrase like shitsurei ni mo, rudely on my part, openly acknowledges the lapse; it is quite formal, and in daily life taihen shitsurei na no desu ga is a more common way to begin.

Notice the endings: wasurete shimaimashite trails off with te instead of finishing the sentence. Leaving it open invites the other person to fill in their name, which feels much gentler than asking a direct question.

Omoidasenai: when you are trying to remember

Wasureta says the memory is gone. Omoidasenai, from omoidasu, to recall, says you are actively searching and cannot find it. This is the natural choice when a word, a title or a restaurant's name is on the tip of your tongue. Oboete inai, I don't remember, is different again: it suggests the thing never really stayed in your memory, and it is common when someone asks about an event you have no recollection of.

For momentary blanks, Japanese has the lovely word dowasure, a sudden lapse on something you know well. Dowasure shichatta tells the listener it is temporary and you will get there. If you are completely stuck on a word, you can describe it instead; there is a separate guide on explaining a Japanese word you cannot remember, which covers those workarounds in detail.

Forgetting to do something

To say you forgot to do an action, turn the verb into a noun with no and mark it with o: denwa suru no o wasureta, I forgot to call. Written Japanese sometimes uses the stem plus wasureru, as in kakiwasureru, forget to write, or iiwasureru, forget to say. Iiwasureta is very handy in conversation when you want to add something you meant to mention.

Reminders use the negative. Wasurenaide is a direct don't forget, and wasurenai yō ni is a gentler make sure you don't forget, often used when giving advice or reminding yourself.

Common mistakes with forgetting

Most errors come from mapping English too directly. English uses forgot for almost everything; Japanese splits the idea by what you forgot and how you feel about it.

• Saying wasuremashita when reminded of something. A, wasurete imashita sounds more natural because you had forgotten until that moment.
• Using de for where you left something. It is densha ni okiwasureta, with ni, because ni marks where the item ended up.
• Using wasureru for a lost wallet. If it may have been dropped or lost, nakushita or otoshita is clearer; wasureta implies you know you simply left it.
• Saying o-namae o wasuremashita bluntly to someone you have met before. Ask again with shitsurei desu ga, or soften it with shimaimashite.
• Overusing shitsunen in casual speech. It belongs in business and formal settings; with friends it sounds stiff.
• Confusing omoidasenai with wasureta. If you are still searching, omoidasenai or nan dakke fits better than a flat I forgot.