Calculation Guides
More than calculators — we explain why the formulas work the way they do, with real-world examples. All guides reflect 2026 rates and regulations.
Gross vs. Net Salary in Korea: Why the Gap? (2026 Guide)
A full breakdown of why your Korean contract salary differs from take-home pay — national insurance, income tax, and non-taxable allowances explained with 2026 rates.
Korean Severance Pay 2026: Calculation and Retirement Tax Explained
How severance is calculated from average wages, 2026 retirement income tax deductions, and IRP rollover tax benefits — with worked examples.
When Does Refinancing a Loan Pay Off? A Break-Even Framework
A break-even formula for loan refinancing that factors in prepayment penalties and rate reduction, illustrated with three real-world scenarios.
5 Reasons BMI Alone Misleads — and What to Measure Alongside
Why BMI misclassifies muscular, elderly, or abdominally obese individuals — and which complementary metrics to use.
Korean VAT Filing for Self-Employed: 2026 Practical Guide
Simplified vs. general VAT, deductible purchases, a pre-filing checklist, and a worked example.
Korea's Unified Age Act: What Changed, What Didn't
Post-2023 age-system changes, and the military/alcohol/school contexts that still use year-age.
Why "30% + 20% Off" Isn't 50% — Discount Stacking Math
Stacked-discount formula, five common traps, and a 3-second mental shortcut for exact combined rates.
Korean Freelancer Withholding: 3.3% vs. 8.8% — The Real Difference
Business income vs. other income in Korea — classification, effective-tax differences, and knock-on effects on health insurance and pension.
The Truth About Exchange Fees: What a 90% Preferential Rate Really Means
Exchange fees hide inside the rate spread. Base rate vs. cash rate, what a 90% preferential rate actually saves, and a KRW 1M scenario-by-scenario comparison.
The Math of Averaging Down: How Much Rebound You Need to Break Even
A -50% loss needs a +100% rebound. We work through the averaging-down formula, how it changes your break-even rebound, and the real break-even after 2026 Korean fees and transaction tax.