Hidden line

Mentor productivity tax

Senior engineers lose roughly 30% of their own output while mentoring, as pairing and review cycles pull them out of deep work. At a $180K fully-loaded mentor that is $4,500 of unrealised output per month - across an 8-12 week ramp it adds up.

Source: This site's mentor-load model

Typical range

$5k-$18k

Hidden line

Team velocity drag

Sprint velocity drops 25-40% when a new engineer joins (Zartis, FullScale). Pairing, code review cycles, and onboarding meetings absorb the surrounding team. The drag fades after week four.

Source: Zartis 2024, FullScale productivity studies

Typical range

$3k-$14k

Hidden line

Salary during ramp

You pay full salary for 5-65% productivity output across 8-22 weeks. The earlier the curve, the larger the gap. Juniors carry the largest absolute productivity gap; seniors the largest weekly dollar gap.

Source: TeamStation 2025, internal ramp models

Typical range

$10k-$32k

Hidden line

Rework and review overhead

New engineers ship 30-40% more bugs in month one, dropping to ~10% by month three (BCG software study). Each rework cycle pulls a reviewer out of focus work and adds days of latency to the ticket.

Source: BCG software-team productivity report 2024

Typical range

$2k-$7k

Hidden line

Tooling and licence costs

IDE, cloud dev environment, observability seats, security tools, design assets, AI assistants. Per-seat first-year cost is rising as orgs adopt Cortex / Backstage / Copilot Business. Fixed cost regardless of seniority.

Source: Public list pricing as of April 2026

Typical range

$1.5k-$10k

Hidden line

Early-attrition risk

22% of developers leave within 90 days (DevPath, Zartis). Replacement cost is 50-200% of salary (SHRM). Even if you do not provision the line, you are running an unhedged actuarial liability.

Source: DevPath, Zartis 2024, SHRM

Typical range

$15k-$50k risk reserve

Hidden line

Delayed feature delivery

Roadmap items the team would have shipped if not absorbed by onboarding load. Hardest to quantify, often the largest. CFOs care more about this line than any other on this page.

Source: Internal product analytics typical

Typical range

Opportunity cost: varies

Aggregated hidden cost

Adds $20k-$50k of unbudgeted spend per hire.

On top of the $5k-$10k visible budget most managers pencil in. Multiply by hires-per-quarter to get the real number on your forecast. The largest single line is usually mentor opportunity cost or delayed feature delivery, depending on company stage.

Common questions

Why is the mentor tax so often missed?+

Because no internal ledger has a 'mentor time' line. The mentor is salaried, present, and apparently productive in meetings. The 30% drag comes from context-switching out of deep work and is invisible in payroll, but very visible in shipping velocity.

How do you quantify the early-attrition risk reserve?+

Multiply replacement cost (50-200% of salary, SHRM) by 22% (DevPath early-attrition rate). For a $160K mid-level engineer that is roughly $35,000 of expected loss across the cohort. Treat it like an insurance reserve.

Is delayed feature delivery a real cost or a vibe?+

It is a real cost - the hardest one to put a dollar on. Most engineering orgs underestimate it because they look at sprint velocity, not roadmap slippage. Companies with mature product analytics can usually pull a per-feature revenue or retention number.

What single fix has the biggest impact?+

Pre-boarding. Eliminating day-one friction (laptop, accounts, repo access, dev container ready) saves 2-5 days of senior mentor time and starts the productivity curve a week earlier.