Editorial principles
- Every formula and figure is verified against official sources (laws and public agency notices).
- When rates change, the calculator and its guide content are updated together.
- Reported errors are fixed as soon as they are confirmed.
Calculators by Sin Dongho (178)
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Health
Pregnancy Due Date Calculator
Free pregnancy due date calculator using ACOG Committee Opinion 700 — Naegele's rule (LMP + 280 days), conception date, or first-trimester ultrasound. Includes weekly milestones.
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Developer Tools
Cron Expression Generator
Build or decode 5-field cron expressions used by Linux crontab, GitHub Actions, AWS EventBridge, Kubernetes CronJobs, and Jenkins. Includes plain-English explanation and next firing times.
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Health
Ovulation Calculator
Free ovulation calculator using ACOG and ASRM guidance. Predicts your ovulation day, six-day fertile window, and the highest-probability conception days based on cycle length.
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Health
Blood Pressure Calculator
Free blood pressure calculator using the 2017 ACC/AHA hypertension guideline. Categorize systolic and diastolic readings into normal, elevated, stage 1, stage 2, or hypertensive crisis.
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Health
BAC Calculator
Free Blood Alcohol Content (BAC) calculator using the Widmark formula. Estimate your BAC after drinking and time until 0.00 — for educational use only, not legal proof of sobriety.
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Health
Sleep Calculator
Find the best bedtime or wake-up time using 90-minute sleep cycles. Based on the National Sleep Foundation recommendation of 7–9 hours and 5–6 complete cycles per night.
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Health
Protein Intake Calculator
Free protein intake calculator using USDA, ACSM, and ISSN guidelines. Get a personalized daily target in grams based on body weight, activity level, age, and goal (muscle, fat loss, longevity).
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Auto
Vehicle Property Tax Calculator
Free vehicle property tax calculator. Estimate annual personal property tax on cars in Virginia, Missouri, Connecticut, Rhode Island, and other states that levy this tax.
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Auto
Vehicle Sales Tax & Out-the-Door Calculator
Free car sales tax calculator. Compute state sales tax, document fees, registration, and total out-the-door price by state. Handles trade-in tax credit (where applicable).
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Auto
Fuel Cost Calculator
Free fuel cost calculator. Compute the cost of any trip or annual fuel spend by MPG, distance, and gas price. Compare multiple vehicles side by side or model an upgrade.
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Auto
EV Charging Cost Calculator
Free EV charging cost calculator. Compare home charging, public Level 2, and DC fast charging cost per mile and per full charge using kWh price and battery capacity.
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Developer Tools
Lorem Ipsum Generator
Free Lorem ipsum placeholder text generator. Generate paragraphs, sentences, or words for design mockups, wireframes, and HTML templates with optional <p> tag wrapping.
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