ToolSelf Blog
Guides on taxes, finance, business, and practical tools for freelancers and everyone.
Date & Time
Timezone Conversion Without Losing Your Mind
IANA timezone database is the source of truth. Three-letter abbreviations like EST and IST are ambiguous and unsafe.
Nov 30, 2025
Math
Quadratic Formula: When Factoring Fails
For ax^2 + bx + c = 0, x = (-b +/- sqrt(b^2 - 4ac)) / 2a. The discriminant tells you what kind of roots to expect.
Nov 26, 2025
Taxes
Tax Deductions for Freelancers: Maximize Your Write-Offs
Most freelancers miss deductions. Here's a comprehensive list of what you can write off: office supplies, software, equipment, and more.
Nov 25, 2025
Date & Time
Working Days Calculator: What Counts as a Business Day
Business days exclude weekends and "federal holidays" — but federal holidays vary by country and by industry.
Nov 25, 2025
Health
TDEE and BMR: How Many Calories Do You Actually Burn?
BMR is what you burn at rest. TDEE adds your activity. Knowing both is the foundation of any sustainable diet.
Nov 23, 2025