Date & time calculators

Date and time calculators on CalcTool

This hub groups free date tools in your browser—no signup. Pick the calculator that matches your question—age, spans, countdowns, business days, clock times, time zones, due dates, and milestone birthdays.

Which tool should I use?

• Age calculator — date of birth and “as of” date → years, months, days old, total days lived, next birthday.
• Age milestone — birth date + target age → date you turn that age and days until or since.
• Date difference — any start and end date → total days, weeks + remainder, calendar years/months/days, and week number for each date.
• Days until — from a start date (often today) to one target → days remaining or days since.
• Add/subtract date — one start date plus or minus an amount in days, weeks, months, or years → new date.
• Business days — add/subtract or count Mon–Fri (weekends excluded; holidays not).
• Time difference — hours and minutes between two clock times.
• Time zone converter — same instant in another IANA zone.
• Due date — LMP → estimated due date and gestational age (280-day rule).

Calendar days vs. business days

Most tools count calendar days (weekends included). Contracts that say “business days” need the business days calculator—Mon–Fri only, no public holiday table here. “90 days” without the word business usually means calendar days; use add/subtract date for that.

How these tools relate

Date difference and days until both measure spans; difference is symmetric between two arbitrary dates, while days until is phrased for a single target. Add/subtract is the inverse problem: you know the start and the offset, not the end. Age is specialized: birth date is the start, and the output is “how old” rather than a generic interval.

Each page includes steps, examples, and FAQs. Copy link on any tool lets you bookmark a scenario or send it to someone else so they see the same inputs and results.

Frequently asked questions