Home to Microsoft and Costco: The 425 Area Code in the Seattle Eastside

The 425 area code covers the Seattle Eastside — the technology-dense suburban corridor east of Lake Washington that includes Bellevue, Redmond (global headquarters of Microsoft), Kirkland, Renton, Bothell, and Issaquah (global headquarters of Costco).

Area code 425 was created in November 1995 when the original 206 code, which had covered all of western Washington since 1947, could no longer sustain the explosive subscriber growth driven by the Pacific Northwest technology boom. No overlay has ever been added to 425; the single code continues to serve the Eastside without a relief code. Time zone is Pacific (PT) throughout.

This guide covers what 425 serves, explains how Lake Washington divides the 206 and 425 codes, outlines Microsoft's outsized presence in the 425 footprint, and details the economy behind one of the most corporation-dense area codes in the United States.

What 425 covers — the Seattle Eastside

The 425 area code location is the Seattle Eastside — the communities on the eastern shore of Lake Washington, directly across from Seattle. Lake Washington acts as the natural geographic boundary between the 206 (Seattle proper) and 425 codes. Mercer Island sits in the lake between the two codes and is served by 206. Everything on the eastern shore from Renton in the south to Kenmore in the north falls under 425.

Cities and communities in the 425 area code:

What 425 does NOT cover:

• Seattle proper → 206 (and 564 overlay)
• Tacoma and south Puget Sound → 253
• Rural western Washington, Olympia, Bellingham → 360
• Eastern Washington (Spokane) → 509

Microsoft in the 425 — Redmond by the numbers

No single institution defines a US area code more completely than Microsoft defines 425. The company's global headquarters has been in Redmond since 1986, when it moved from a smaller office in Bellevue to the campus that now spans more than 500 buildings across the north Redmond plateau.

Microsoft by the numbers in Redmond:

• 221,000+ employees worldwide, with the largest single concentration on the Redmond campus — more than 50,000 employees on-site or in the immediate 425 corridor
• $3+ trillion market capitalization — Microsoft has traded as the most valuable company in the world by market cap at various points in 2024–2026, alongside Apple
• Redmond campus since 1986 — 40 years of continuous growth, expanding from the original 30-acre site to a self-contained corporate city with its own road network, sports facilities, restaurants, and shuttles
• Xbox, Azure, Teams, LinkedIn, GitHub — all of the company's major consumer and enterprise product lines are led from the 425 footprint
• AI investment at scale — Microsoft's $10+ billion investment in OpenAI and the integration of AI across its products has made Redmond one of the most consequential AI development campuses in the world

Beyond Microsoft, Redmond hosts Nintendo of America's North American headquarters, and the surrounding Eastside corridor has attracted satellite offices from virtually every major technology company.

How area code 425 was split from 206

January 1, 1947 — Washington state launched with two original NANP codes: 206 for western Washington (Seattle and west of the Cascades) and 509 for eastern Washington (Spokane and the eastern plateau). Area code 206 covered the entire Puget Sound region — Seattle, Tacoma, Bellevue, Redmond, and every other western Washington community under a single three-digit code.

February 3, 1995 — 253 splits for Tacoma The south Puget Sound corridor — Tacoma, Auburn, Federal Way — was the first to be split off from 206 as 253. The mobile phone explosion of the early 1990s had pushed the 206 pool toward rapid exhaustion, and the Tacoma region was separated first given its geographic distinctness from Seattle.

September 3, 1995 — 360 splits for rural western Washington Rural western Washington — from Olympia in the south through Bellingham and the Olympic Peninsula to the Oregon border — was carved out as 360. This removed the low-density western Washington subscriber base from the 206 pool, but number exhaustion in the high-density Seattle-Eastside corridor continued accelerating.

November 4, 1995 — 425 created for the Seattle Eastside With the Seattle metro's suburban and corporate subscriber growth still outpacing what remained in the 206 pool, the Eastside corridor was split off as 425. Bellevue, Redmond, Kirkland, Renton, Bothell, and Issaquah moved to the new code. Area code 206 contracted to serve Seattle proper — the footprint it holds today. Just as 423 was created that same year from Tennessee's 615, 425 was part of a nationwide wave of area code splits triggered by the 1990s mobile boom.

What the 425 economy runs on

The 425 area code hosts a concentration of Fortune 500 headquarters and globally recognized brands that few suburban area codes anywhere in the world can match:

Microsoft (Redmond) Covered in depth above — Microsoft's Redmond headquarters employs tens of thousands within the 425 footprint and anchors the entire Eastside tech economy. The Redmond campus's influence extends to the entire 425 labor market: the average tech salary in the Bellevue-Redmond corridor is among the highest in the United States, and housing, retail, and services across the Eastside are shaped by the Microsoft employment base.

Costco Wholesale (Issaquah) Costco — the second-largest retailer in the United States by revenue — has been headquartered in Issaquah since 1996. With more than $240 billion in annual revenue and over 900 warehouse locations globally, Costco is one of the most successful retail models in history and is the defining institution of the southern 425 corridor. Contact us to explore 425 numbers for your Seattle Eastside business presence.

Boeing Renton Plant Boeing's Renton assembly facility is one of the most significant manufacturing sites in the Pacific Northwest. The plant is the final assembly location for the Boeing 737 and 737 MAX, the world's best-selling commercial aircraft family. With more than 10,000 direct employees on-site, the Renton plant is the 425 footprint's largest single manufacturing employer and a cornerstone of King County's industrial tax base.

Valve Corporation (Kirkland) Valve Corporation — creator of the Steam digital gaming platform (130+ million active users), the Half-Life series, Portal, Dota 2, and Counter-Strike — maintains its global headquarters in Kirkland. Valve is one of the most valuable private technology companies in the United States, with Steam controlling approximately 75% of the PC gaming market. Its quiet Kirkland presence is characteristic of the Eastside's tendency to house globally significant technology companies with a low public profile relative to their market power.

Is 425 in California or Texas?

No — 425 is a Washington state area code, serving the Seattle Eastside. It is not assigned in California, Texas, or any other state.

"425 area code California" searches reflect the high volume of outbound calls that Microsoft, Costco, and Boeing generate to California business counterparts — particularly to Silicon Valley technology and aerospace partners. A California recipient receiving a call from a 425 Microsoft or Costco number may search their own state to identify the origin. The answer is always the same: 425 is the Seattle Eastside in Washington state.

"425 area code Texas" follows the same pattern. Costco's rapid Texas expansion and Boeing's defense partnerships with Texas-based contractors generate high-volume 425-to-Texas call traffic, driving recipients to search the unfamiliar code.

"1 425 area code" is the international dialing format: +1 is the United States country code, and 425 is the Bellevue-Redmond area code. International callers reaching Microsoft's Redmond campus or Costco's Issaquah headquarters encounter the +1 425 format regularly.

425 area code ZIP codes

Common ZIP codes within the 425 coverage area:

Bellevue 98004 · 98005 · 98006 · 98007 · 98008 · 98009 · 98015

Redmond 98052 · 98053 · 98073 · 98074

Kirkland 98033 · 98034 · 98083

Renton 98055 · 98056 · 98057 · 98058 · 98059

Bothell 98011 · 98012 · 98021

Issaquah 98027 · 98029 · 98075

Sammamish 98074 · 98075

Woodinville 98072 · 98077

Kenmore 98028

Mercer Island 98040

Note: Seattle ZIP codes (98101–98199 range) use area code 206, not 425. The boundary follows Lake Washington and the Seattle city limits.

Scam calls from 425 numbers

Robocallers spoof 425 numbers specifically because the area code is associated with Microsoft, Costco, and Boeing — three institutions with global recognition that lend spoofed calls an air of legitimacy. Common spoofed 425 schemes include:

• Microsoft tech support scams — The most prevalent 425 spoof: callers claim to be Microsoft security teams, Windows support, or Xbox billing departments, using a spoofed Redmond-area 425 number as a credibility signal. Microsoft never initiates unsolicited support calls.
• Costco membership and prize scams — Fraudulent calls claiming the recipient won a Costco prize, has a membership billing issue, or has been selected for a special offer requiring immediate confirmation.
• Boeing HR and job scams — Fake Boeing recruiting or HR calls targeting job seekers, offering positions that require upfront fees or personal information.
• General tech support impersonation — Any call claiming to be from a "local Seattle-area tech company" using a spoofed 425 number to appear more credible than an out-of-state number.

The FCC's STIR/SHAKEN call authentication protocol requires carriers to verify caller ID before connecting. Any 425 call claiming to be Microsoft, Costco, or Boeing that was not initiated by you and leaves no verifiable callback number is almost certainly a spoof — all three companies explicitly state they do not initiate unsolicited phone contact for support or prizes.

Key takeaways

• 425 is the Seattle Eastside area code — Bellevue, Redmond, Kirkland, Renton, Bothell, Issaquah — in service since November 1995 when it split from the original 206 western Washington code.
• Lake Washington is the physical boundary between 206 (Seattle proper, west shore) and 425 (Eastside, east shore).
• 425 has no overlay. The single code has served the Eastside since 1995 without a relief code.
• Microsoft global headquarters is in Redmond, 425 — 221,000 employees, $3T+ market cap, 500+ campus buildings since 1986.
• Costco global headquarters is in Issaquah, 425 — $240B+ revenue, #2 US retailer.
• 425 is not in California or Texas — it is exclusively Washington state; high outbound volume from Microsoft and Costco drives those search queries.
• Time zone: Pacific (PT) — PST (UTC −8) in winter, PDT (UTC −7) during Daylight Saving Time.

Frequently asked questions