ISO Week Number & Week Calendar
Get the ISO week number for any date and browse the full Monday–Sunday calendar.
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Online calculators & handy tools
Fast, privacy-friendly, and accurate. Use the filters to find the right tool.
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Age Calculator
Exact age from a birth date — years, months, days, plus next birthday & weekday insights.
Days Between Dates
Total days, weeks, months, and optional business days between two dates. Time fields supported.
Countdown
Create a live countdown to any date/time with time-zone control and a shareable link.
Mail Delivery Time (ZIP to ZIP)
Estimate USPS delivery time by ZIP pair and mail class. Weekends & US holidays handled.
Significant Figures Calculator
Count sig figs, see which digits are significant, and get rule-by-rule explanations.
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About Daydelta tools
How we build
Each tool is a lightweight, static page with minimal JavaScript for instant results. We show formulas and edge cases to keep things transparent.
Accuracy & limitations
Calculations are tested against known examples. Some tools may simplify complex regulations or omit country-specific rules. Use for education—not professional advice.
Privacy-friendly
No sign-ups, no unnecessary cookies. Results are computed in your browser. Read our Privacy Policy.
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