US Tax Services

Offshore Tax Support for US CPA Firms.

Optimus Tax & Accounting LLP is a trusted offshore tax support partner for US CPA firms, CFO advisory practices, and accounting firms. We integrate seamlessly into your existing workflow — handling the preparation, documentation, and compliance workload so your team can focus on high-value advisory and client relationships. Every deliverable is CPA-reviewed, IRS-compliant, and ready for your final sign-off.

Who We Serve

Built for the firms scaling US tax compliance.

  • US CPA firms looking to scale capacity without increasing headcount
  • CFO advisory and outsourced CFO practices needing reliable tax prep support
  • Accounting firms managing high-volume individual and business tax returns
  • Mid-size firms handling multi-state, cross-border, and complex filings
  • Growing practices needing overflow support during peak tax seasons

Our US Tax Services

Eleven dedicated service categories, every one CPA-reviewed.

01

Individual Tax Return Preparation (Form 1040)

  • Preparation of individual returns for your firm's client base
  • Wages, self-employment, rental, investment, and foreign income
  • Multi-state filings and apportionment handled accurately
  • Deductions, credits, and tax optimization applied
  • CPA-reviewed workpapers delivered ready for your sign-off
02

Nonresident Tax Compliance (Form 1040-NR)

  • U.S. tax residency determination under the substantial presence test
  • ECI/FDAP income reporting and withholding compliance
  • Tax treaty analysis and benefit application
  • Preparation support for nonresident clients of your firm
03

Business Tax Return Preparation

  • Corporations — Form 1120 preparation and support
  • S-Corporations — Form 1120-S with shareholder reporting
  • Partnerships — Form 1065 with Schedule K-1 preparation
  • Single-Member & Multi-Member LLC returns
  • Multi-state income tax compliance and apportionment
04

Payroll Tax Filings & Compliance

  • Forms 941, 940, W-2, and W-3 preparation
  • Payroll tax calculations and compliance review
  • Independent contractor 1099-NEC and 1099-MISC preparation
  • Timely filings to protect your clients from IRS penalties
05

Tax Workpaper & Documentation Preparation

  • Detailed schedules and supporting workpapers for every return
  • Audit-ready documentation prepared to your firm's standards
  • Organized files for seamless CPA review and sign-off
  • Consistent formatting aligned with your internal processes
06

IRS Notice & Correspondence Support

  • Documentation preparation for IRS and state tax notice responses
  • Supporting your team in resolving client tax assessments
  • Organized correspondence ready for CPA review and submission
07

Year-End Tax Adjustments & Reconciliations

  • Year-end adjusting entries and tax account reconciliations
  • Books aligned with tax return requirements
  • Audit-ready year-end close delivered on time
08

Sales Tax Compliance & Multi-State Filing Support

  • Nexus analysis and state registration support
  • Sales tax calculations and periodic filing preparation
  • Multi-state compliance management for your business clients
09

Trust & Estate Tax Returns (Form 1041)

  • Preparation of fiduciary income tax returns for trusts and estates
  • Simple, complex, and grantor trust return preparation
  • Schedule K-1 preparation for trust and estate beneficiaries
  • Estate administration tax support and year-end fiduciary reporting
  • Coordination with your CPA team for seamless trust tax compliance
10

State Income Tax Compliance

  • State income tax return preparation across all required jurisdictions
  • Nexus determination and multi-state filing obligation analysis
  • Income sourcing, apportionment, and allocation calculations
  • State-specific credits, deductions, and compliance requirements
  • Timely state filings to avoid penalties and interest for your clients
11

Cross-Border & International Tax Support

  • Foreign-owned US entity compliance and reporting
  • FBAR and Form 8938 documentation support
  • Treaty benefit analysis and cross-border structuring support
  • EIN application and US LLC compliance setup support
How We Work

How we work with your firm.

Onboarding

Simple, structured setup tailored to your firm's workflow and standards.

Secure Data Collection

Client documents received via secure file-sharing systems with strict confidentiality.

Expert Preparation

Experienced tax professionals prepare returns and workpapers to your specifications.

CPA Review & Delivery

All work is internally reviewed before delivery — ready for your final sign-off.

Ongoing Support

Year-round availability for overflow work, complex filings, and peak season surge.

Why Optimus

Why partner with Optimus?

  • Scale your practice capacity without adding full-time staff.
  • CPA-supervised output — every deliverable reviewed before handoff.
  • Consistent quality across high-volume and complex filings.
  • Secure systems, strict NDAs, and full client confidentiality.
  • Dedicated team assigned to your firm — not a rotating pool.
  • Competitive offshore pricing — significantly lower than local hiring.
  • Flexible engagement — project-based, seasonal, or ongoing retainer.
Get Started

Ready to hand off your next tax season?

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