Senior Software Engineer, Payroll Engine

Senior Software Engineer, Payroll Enginede Anda portfolio companyTeam: PayrollLevel: Senior (IC)Location: Remote (U.S.)Start: early November 2026Compensation: $100,000–$105,000THE ROLEYou own the heart of the product: the payroll domain model, the append-only ledger, and the pay-run engine that takes a run from draft to committed check. Your code decides what people get paid. The exit criterion for your first four months is that the engine reproduces a corpus of real pay runs from the incumbent system to the cent.WHAT YOU WILL DO• Design and build the domain model: pay groups and calendars, earning and deduction codes with limits and ordering, employee tax profiles, year-to-date and quarter-to-date accumulators per EIN.• Build the ledger as an append-only record of every committed check and adjustment, the single source for registers, general ledger, year-end and audit.• Build the pay-run state machine: draft, preview, calculate, approve, commit; regular and off-cycle runs; manual checks; voids and reversals; retroactive pay.• Implement gross-to-net orchestration around the tax adapter: pre-tax and post-tax deductions, imputed income, supplemental wages, garnishment calculation with withholding limits.• Build the generic hours-and-earnings import, then the bridge from the portfolio company's time-and-attendance product that turns locked, approved timecards into earnings lines with rate, pay code, work location and job-cost dimensions.• Build and maintain the regression harness: replay the corpus on every change, report variances to the cent, and run every variance to ground.• Write Technical Documents from the product manager's PRDs, direct coding agents against them, and review every agent-authored PR line by line before merge.• Keep money as integer cents and committed runs immutable; make every calculation re-runnable from stored inputs and engine version.MUST HAVE• 5+ years building transactional backend systems in Python; Django and PostgreSQL in production.• Has shipped a system where money is the output: payroll, billing, banking, insurance claims, accounting. You can explain how you kept a ledger correct under concurrency and corrections.• Fluent in integer-cents arithmetic, rounding rules, and the difference between a correction and a reversal.• Designs state machines and event-sourced or append-only data models; knows why committed records are never edited.• PostgreSQL depth: migrations against live data, constraints, transactions, advisory locks or equivalent.• Writes tests as part of the change; has built or maintained a replay or golden-file regression suite.• Has worked with AI coding agents on real deliverables: writes specs an agent can execute and reviews agent output critically.• Comfortable in a monorepo with CI, Docker Compose and GitHub Actions.NICE TO HAVE• U.S. payroll domain: pay codes, pre/post-tax ordering, YTD limits, FLSA overtime, garnishment priority rules, multi-EIN employers.• GraphQL schema design (Graphene) and React/Apollo for the pay-run UI.• Celery or equivalent for long-running calculation jobs.• Time and attendance or scheduling domain; job costing and labor allocation.• Experience maintaining AGENTS.md-style conventions for a team.NOT A FIT• CRUD-app backgrounds with no financial or transactional system experience.• Engineers who treat floating-point money as fine until it isn't.• Someone who treats agent output as done once it compiles.• Someone who wants a green-field stack; this lives inside the portfolio company's existing time-and-attendance codebase.