Time Calculator
⏱️ What is the Time Calculator?
Need to figure out what time it will be 3 days and 5 hours from now? Or perhaps you're trying to work backwards from a deadline to set reminders? This time calculator handles all that math for you, complete with timezone awareness and daylight saving time detection.
Unlike basic calculators that only work with hours or days, this tool lets you combine multiple time units in a single calculation. Add 2 weeks, subtract 3 days, then add 6 hours - all in one go. The result updates instantly as you adjust your operations.
🔧 Core Features
- Flexible Time Input: Use the date picker or type directly. Supports multiple date formats automatically.
- Multiple Operations: Stack as many add/subtract operations as you need. Mix different time units freely.
- Full Timezone Support: Over 400 IANA timezones available. See results in any timezone, regardless of input.
- DST Detection: Get warnings when your calculation crosses daylight saving time boundaries.
- Output Formats: ISO-8601, RFC 2822, Unix timestamp, human-readable, or your own custom format.
- Reverse Calculation: Flip your calculation around - turn the result into the new starting point.
- Calculation History: Recent calculations are saved so you can reference or reload them.
📋 Supported Time Units
| Unit | Equivalent | Common Use |
|---|---|---|
| Seconds | Base unit | Precise timing, API timeouts |
| Minutes | 60 seconds | Meeting durations, short delays |
| Hours | 3,600 seconds | Work shifts, timezone offsets |
| Days | 86,400 seconds | Deadlines, scheduling |
| Weeks | 604,800 seconds | Sprint planning, recurring events |
💡 Practical Examples
🚀 Project Deadline Planning
Starting a 2-week sprint on Monday? Set your base time to the sprint start, add 2 weeks, and you'll see exactly when the sprint ends - including the day of the week and accounting for any DST changes that might occur.
🔍 Log Analysis
Investigating an incident that happened "about 3 hours before the alert"? Take the alert timestamp, subtract 3 hours, and get the approximate window to search in your logs. Works across timezone boundaries too.
🌍 International Meeting Scheduling
Planning a call with teams in Tokyo, London, and New York? Enter your proposed time in one timezone, then switch the output timezone to see what time it would be for each participant.
⏰ Token/Certificate Expiry
Got an API token that expires in 30 days? Enter today's date, add 30 days, and you'll know exactly when to renew it. Set the output to Unix timestamp if you need to configure the expiry programmatically.
🌐 Understanding Daylight Saving Time
DST can make time calculations tricky. When clocks "spring forward," an hour disappears. When they "fall back," an hour repeats. This calculator detects when your calculation crosses these boundaries and warns you.
Example DST Scenario:
If you add exactly 24 hours starting at 1:00 AM on the day DST ends in New York, you might expect to land at 1:00 AM the next day. But because clocks fall back, you'd actually arrive at 12:00 AM (midnight) - effectively 25 hours of "wall clock" time have passed.
This calculator uses fixed durations (1 day = exactly 86,400 seconds), which is the standard approach for most applications. The DST warning helps you recognize when this might affect your specific use case.
📝 Custom Format Patterns
When you select "Custom" output format, you can use these strftime patterns:
%Y - Year (2024)%m - Month (01-12)%d - Day (01-31)%H - Hour 24h (00-23)%I - Hour 12h (01-12)%M - Minute (00-59)%S - Second (00-59)%p - AM/PM%A - Weekday name%B - Month name%Z - Timezone name%z - UTC offsetExample patterns:
%Y-%m-%d %H:%M:%S→ 2024-01-15 14:30:00%B %d, %Y→ January 15, 2024%A at %I:%M %p→ Monday at 02:30 PM
❓ Tips & Troubleshooting
Why doesn't adding 1 month work?
Months have varying lengths (28-31 days), which creates ambiguity. Should "January 31 + 1 month" be February 28 or March 3? To avoid confusion, this calculator uses fixed units only. For month calculations, consider using 30 days as an approximation.
The result shows a different day than expected
Check your timezone settings. If your base time is in one timezone but you're viewing results in another, the date might shift. Also verify whether DST is affecting the calculation.
How do I calculate "business days"?
This calculator uses calendar days, not business days. For 5 business days, you'd need to add 7 calendar days (assuming no holidays) or calculate manually accounting for weekends.
What's the valid date range?
The calculator works reliably for dates roughly between years 1970 and 2100. Extreme dates may cause errors or unexpected results.
🔗 Related Tools
- Unix Timestamp Converter - Convert between Unix timestamps and human-readable dates with timezone support
- Elapsed Time Calculator - Calculate duration between two dates in seconds, minutes, hours, days, months, and years
- Cron Expression Parser - Parse and validate cron expressions with next execution times, timezone support, and human-readable descriptions
- Timestamp Log Sorter - Parse, sort, and convert timestamps in log files with auto-detection for ISO-8601, Unix, and RFC 2822 formats