Senior Software Engineer, Payroll Engine
Job Description
Senior Software Engineer, Payroll Engine
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de Anda portfolio company
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Team: Payroll
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Level: Senior (IC)
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Location: Remote (U.S.)
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Start: early November 2026
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Compensation: $100,000–$105,000
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THE ROLE
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You 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.
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WHAT YOU WILL DO
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• 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.
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• 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.
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• Build the pay-run state machine: draft, preview, calculate, approve, commit; regular and off-cycle runs; manual checks; voids and reversals; retroactive pay.
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• Implement gross-to-net orchestration around the tax adapter: pre-tax and post-tax deductions, imputed income, supplemental wages, garnishment calculation with withholding limits.
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• 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.
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• Build and maintain the regression harness: replay the corpus on every change, report variances to the cent, and run every variance to ground.
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• 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.
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• Keep money as integer cents and committed runs immutable; make every calculation re-runnable from stored inputs and engine version.
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MUST HAVE
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• 5+ years building transactional backend systems in Python; Django and PostgreSQL in production.
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• 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.
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• Fluent in integer-cents arithmetic, rounding rules, and the difference between a correction and a reversal.
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• Designs state machines and event-sourced or append-only data models; knows why committed records are never edited.
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• PostgreSQL depth: migrations against live data, constraints, transactions, advisory locks or equivalent.
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• Writes tests as part of the change; has built or maintained a replay or golden-file regression suite.
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• Has worked with AI coding agents on real deliverables: writes specs an agent can execute and reviews agent output critically.
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• Comfortable in a monorepo with CI, Docker Compose and GitHub Actions.
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NICE TO HAVE
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• U.S. payroll domain: pay codes, pre/post-tax ordering, YTD limits, FLSA overtime, garnishment priority rules, multi-EIN employers.
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• GraphQL schema design (Graphene) and React/Apollo for the pay-run UI.
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• Celery or equivalent for long-running calculation jobs.
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• Time and attendance or scheduling domain; job costing and labor allocation.
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• Experience maintaining AGENTS.md-style conventions for a team.
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NOT A FIT
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• CRUD-app backgrounds with no financial or transactional system experience.
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• Engineers who treat floating-point money as fine until it isn't.
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• Someone who treats agent output as done once it compiles.
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• Someone who wants a green-field stack; this lives inside the portfolio company's existing time-and-attendance codebase.