CodeKitHubCalculators
How to compute 13th month pay in the Philippines (and why it's not just your monthly salary)
The DOLE formula for 13th month pay under Presidential Decree No. 851: total basic salary earned this year divided by 12, with worked examples for full-year, partial-year, and unpaid-leave cases, plus the ₱90,000 tax-exempt cap.
Why +50% then −50% doesn't get you back to where you started
A stock rises 50%, then falls 50% — you'd expect to break even, but you're down 25%. Here's the asymmetry behind percentage changes, and why it matters for discounts, salaries and investments.
How we keep our tax and payroll calculators from quietly going stale
Tax rates, social insurance percentages and minimum wages change every year — a calculator with last year's numbers is worse than no calculator at all. Here's the automated system we built to catch that before users do.
Why ovulation isn't "day 14" — how your fertile window is actually calculated
The most repeated fact about the menstrual cycle — ovulation happens on day 14 — is wrong for most people. Here's where the number comes from, why cycle length changes everything, and how to actually estimate your ovulation day and fertile window.
How many calories should you eat per day? BMR vs TDEE, explained simply
Most calorie advice skips the two numbers that actually matter: your BMR (what your body burns at rest) and your TDEE (what you burn in real life). Here's how they differ, how they're calculated, and which one to use for losing, maintaining or gaining weight.
Cheapest LLM API in 2026: full pricing comparison, 19 models
OpenAI, Anthropic, Google, DeepSeek, Qwen, Kimi, GLM and Grok, ranked from cheapest to most expensive on a blended per-token cost. The price gap between the cheapest and priciest model is over 60x.
Why LLM API output tokens cost 4-8x more than input tokens
OpenAI, Anthropic and Google all price output tokens several times higher than input tokens — the same pattern across every provider. Here's the actual reason, and what it means for how you should write prompts.