/Companies

Firstbase.io

YC W21

New York City, US · Founded 2019 · 50 employees · Hiring · 8 known investors

Find your way into Firstbase.io

Each arrow is one introduction. Sign up to fill in the first one.

10,409 people can intro you to Mark

Ask Garry Tan to introduce you to Mark Milastsivy

You →Garry · together at YC W21 →Mark

Sign up to find every way you can get introduced to Firstbase.io

  • Your email: who you already know at Firstbase.io, and who your contacts know
  • 2nd- and 3rd-degree connections: people you know who worked, studied or invested with the Firstbase.io team
  • Your LinkedIn: the connections who can make the intro for you

We rank every route by how warm it is, so you raise on warm intros instead of cold emails.

Firstbase builds an all-in-one business operations platform that automates back office tasks for founders globally, including company incorporation, management, and growth services.

Also known as Firstbase · Firstbase.io, Inc.

Enterprise SoftwareSaaSB2BLegalTechUnited States of AmericaAmerica / CanadaFully Remote

Founders & leadership· Y Combinator alumni (W21)

Firstbase.io was founded in 2019 by Mark Milastsivy.

MMMark Milastsivy
Mark MilastsivyFounder & CEO2019–2025Mark Milastsivy is founder and CEO of Firstbase.io, based in New York City.

Investors · 8

Funding

SEC filings, press & company announcements

Source: company announcements and press reports — follow each round's link for the claim.

Company profile

researched Aug 2026

Firstbase.io operates a software platform that handles the formation and ongoing back-office administration of US companies. Its core formation product lets founders register an LLC or C-Corp through an automated workflow, and is complemented by modules for compliance, accounting, tax filing and business mail. The company positions the offering as a single "startup operating system" intended to replace multiple separate vendors and manual paperwork.

The product line includes Firstbase Start (LLC or C-Corp formation), Mailroom (a premium physical US address and virtual mailbox), Agent (registered agent services, franchise tax and annual report filings across states), Accounting (a bookkeeping platform with full-service accrual bookkeeping and accrual-basis financial statements), Tax Filing (state and federal corporate and personal returns for both US-based and international founders), plus Loop, Payroll, Sales Tax and an Incorporation API. Firstbase One bundles the accounting, compliance, virtual address and tax products into one package, marketed with a stated saving of $1,950 versus separate purchases. Post-formation tooling includes equity assignment with one-click cap table creation in Carta and 83(b) filing.

Alongside the paid products, Firstbase offers a rewards and perks marketplace stated to be worth up to $350,000, including a banking marketplace for US bank account approval, waived Stripe processing fees on a customer's first $20,000 in transactions, and up to $6,000 in law firm credits. The company also publishes free founder resources such as a VC database, incorporation checklist, compliance guide, business name check and various generators.

Business model

Firstbase sells company formation and recurring back-office services directly to founders. Individual products (formation, registered agent, mailbox, accounting, payroll, sales tax, tax filing) are sold separately or bundled as Firstbase One, and an Incorporation API is offered for programmatic use. A promotional offer waives the formation fee so customers pay only the state fee.

Product and subscription fees for incorporation, registered agent and compliance filings, virtual address/mailroom, bookkeeping, payroll and tax filing services, with a bundled package (Firstbase One) advertised at a discount to the sum of individual products.

Traction

The company reports more than 30,000 companies started through its platform, customers in 191 countries, and roughly $3 billion in aggregate funding raised by its customers.

▸Full profile — market position, technology, go-to-market, geography

Market position

Firstbase presents itself as a next-generation business operations platform for founders, citing more than 30,000 companies incorporated and customers spanning 191 countries. Public endorsements on its site come from Carta CEO Henry Ward, Y Combinator partner Jared Friedman, and founders including Tyler Tringas and Danny Olinsky.

Consolidation of formation, registered agent/compliance, mail, bookkeeping and tax filing into one platform rather than eight separate tools; automation of filings for speed and accuracy relative to traditional service providers; support for non-US founders; and human support available globally.

Technology

A web platform that automates the company formation workflow and centralizes back-office operations, with a unified transactions dashboard for accounting, automated compliance reminders and annual report filings, and an Incorporation API. Integrations include Carta for cap table creation and Stripe for payments.

Go-to-market

Self-serve online signup for formation and existing-company onboarding, supported by a promotional offer covering formation fees, 24/7 global human support, partner integrations and perks (banking, payments, legal, equity), founder-oriented content and free tools, and an Incorporation API for partners.

Startup founders and small business owners forming or operating US entities, including international founders outside the United States who need a US company, address, compliance coverage and tax filings.

Geography

Headquartered in the United States and serving founders internationally; the company states it is trusted by founders in 188 countries and that companies incorporated through it represent 191 countries, with registered agent and compliance coverage across US states.

Compiled by commissioned research from 1 cited public sources — announcements, filings, and press listed under research sources below.

Key figures

latest reported
Companies incorporatedJan 202530,000 companies
Countries represented by customersJan 2025191
HeadcountAug 202657
Partner perks value available to customersJan 2025$350K
Total funding raised by customersJan 2025$3B

Company-reported or press-reported figures, each dated to when it was claimed — not independently audited.

Related companies · 10

LegalZoom.com, Inc.This is an educational article on the LegalZoom website explaining what a limited liability company (LLC) is, including its types, tax treatment, formation process, and legal considerations. LegalZoom provides online legal services to help small and mid-size businesses register and manage LLCs and other business structures.
CaribouCaribou provides transfer pricing services and tax compliance support for scaling companies, handling transfer pricing design, accounting entries, VAT, permanent establishment, and R&D eligibility in a single engagement.
IntuitIntuit develops financial software products—including TurboTax, Credit Karma, QuickBooks, and Mailchimp—for consumers and small businesses to manage taxes, credit, accounting, and marketing. It serves approximately 100 million customers worldwide.
OpenIntakeOpenIntake provides AI-powered intake automation for law firms that captures and converts phone inquiries into client matters around the clock.
LexiLexi builds AI-powered systems for legal teams to automate legal work tasks. The platform enables lawyers to focus on strategic and client-facing work rather than routine administrative functions.
UpcounselUpCounsel offers an online platform for businesses to work with lawyers, providing tools for team messaging, document storage and e-signature, time tracking, and invoicing and payment management for legal engagements. It is aimed at companies managing their legal work and communication with attorneys.
&AI&AI uses large language models to analyze patent documents and patent litigation processes, reducing the technical complexity and inefficiencies in patent validity assessment and infringement analysis. The platform targets asset holders, patent litigators, funders, and clients involved in patent-related disputes.
MarqVisionMarqVision provides brand protection and intellectual property management services using AI technology for creators, developers, and artists globally. The platform helps innovators identify and defend against threats to their intellectual property and livelihoods.
ZenbusinessZenBusiness provides an all-in-one platform combining AI-powered guidance (Velo) with customer support to help entrepreneurs start, protect, and grow their businesses through business formations and compliance services. The platform serves business owners at all stages, from first-time LLC filers to established companies managing bookkeeping and regulatory requirements.
StripeStripe provides financial infrastructure for businesses to accept payments, offer financial services, and implement custom revenue models across international markets in 135+ currencies.

Companies working in the same space as Firstbase.io.

In the news

▸Research sources · 1

primary sources listed

1 public sources were cited for this profile; the first-party ones are listed here.

Frequently asked questions

What does Firstbase.io do?
Firstbase is an all-in-one platform for incorporating and running a US company, covering compliance, bookkeeping and taxes.
Who founded Firstbase.io?
Firstbase.io was founded by Mark Milastsivy in 2019.
Who are Firstbase.io's investors?
Firstbase.io's investors include Amino Capital, Quest Ventures, Software Holdings Pty, StartersHub, Utopian Ventures, Y Combinator, Andreessen Horowitz, Kleiner Perkins.
Where is Firstbase.io headquartered?
Firstbase.io is headquartered in New York City, US.