日本語道場 — Nihongo Dojo

～ついでに

~tsuide ni

while at it, on the occasion of

When to use it

Use ～ついでに when one action creates a convenient opportunity to do a second, secondary thing — the clause before ついでに is the main errand, the clause after is the add-on. In business writing and email it softens a request or report by framing it as low-cost ("since I'll be there anyway"). Avoid it when the second action is the real purpose or is a favor asked of a superior, since it can sound like their trouble is being trivialized; ～を機に or ～に合わせて are the neutral formal alternatives.

Formation

Verb (dictionary form) + ついでに — 行くついでに (the two actions overlap / add-on is planned)
Verb (た form) + ついでに — 行ったついでに (main action already underway or completed)
Noun + の + ついでに — 出張のついでに、買い物のついでに（動作性の名詞に限る）
い-adjectives / な-adjectives: not used
Adverbially on its own: ついでに、〜も ("and while we're at it, ...")

Examples

While I'm in Osaka on business, I'll stop by the branch office too.
While booking the meeting room, I went ahead and arranged the equipment.
When I come to pay my respects, I'll bring the quotation along.
When I send the contract, I'll also follow up on the other matter.
While we're on the subject, I'll also explain next term's budget proposal.