Every startup runs on the same four tools, whether the team is two people in a garage or forty people across three time zones: a spreadsheet that holds the model everyone argues about, a document that becomes the deck's backbone, a deck that has to look like it took longer than it did, and an inbox that never actually empties. None of that work is the reason anyone joined a startup. It's the tax on doing the real work.

That's exactly where Claude now lives. Not as a separate app you have to remember to open, but as a sidebar inside Excel, PowerPoint, Word, and Outlook — reading what's already open, respecting your formulas and templates, and making changes you review before anything ships. According to Microsoft's 2026 Work Trend Index, nearly half of all AI conversations at work are now spent on analysis and problem-solving rather than busywork, and the number of active AI agents running across Microsoft 365 grew 15x in a single year. Founders who are still doing every model, memo, and deck by hand aren't just working harder than they need to — they're falling behind a curve that's moving fast.

That 49% is the headline for a founder: the biggest use of AI at work isn't drafting or searching, it's thinking through problems — which is precisely what a lean team has the least spare time to do properly. This guide walks through how to install Claude in each of the four Microsoft 365 apps, and what you can actually get done once it's there.

A ten-person startup doesn't have a dedicated analyst, a paralegal, or an executive assistant. Whoever is building the model is also writing the deck, and whoever is writing the deck is also clearing their inbox before the investor call. Claude for Microsoft 365 doesn't replace any of those people — it removes the parts of the job that were never really about judgment: rebuilding a formula chain after a founder changes one assumption, reformatting a slide to match a template for the fifth time, chasing down what a redlined term sheet actually changed, or triaging fifty emails before a fundraising call.

The four add-ins also talk to each other. Claude can pull the latest numbers from an open Excel model straight into a Word memo or a PowerPoint slide, or read an email thread in Outlook and use it as context while drafting in Word — all in one conversation, without you copying and pasting between windows. For a small team juggling every function at once, that's the real unlock: less time spent being the glue between your own tools.

Claude for Excel installs as an add-in and works inside the workbook you already have open — it can explain how a number was calculated, adjust assumptions while keeping every downstream formula intact, and build models from scratch.