Last week I scheduled a meeting for 3 PM my time, forgetting my client was in Tokyo. They joined the call at 5 AM their time – not exactly the best way to maintain a business relationship. Sound familiar?

After testing over 30 timezone tools this month, I found the ones that actually work. Here are the 8 best options for 2025.

Quick Overview: Best Tools by Use Case

Best Overall: World Time Buddy
Best Free Option: Datetime.app
Best for Teams: Every Time Zone
Best Mobile App: Time Zone Converter by TimeandDate
Best for Developers: Spacetime

1. World Time Buddy

World Time Buddy remains the gold standard for timezone conversion. The interface shows multiple time zones side by side with a draggable time slider that instantly shows corresponding times across all zones.

Pros:

Visual timeline makes scheduling intuitive
Handles DST changes automatically
Free version covers most needs
Mobile apps available

Cons:

Premium features cost $39/year
Can be slow with many timezones
Limited customization options

Best for: Freelancers and small teams scheduling regular international calls.

Pricing: Free for 3 timezones, $39/year for unlimited

2. TimeandDate.com

TimeandDate.com offers comprehensive timezone features beyond simple conversion. Their meeting planner specifically helps find optimal meeting times across multiple zones.

Pros:

Completely free
Extensive database of cities
Shows DST transitions clearly
No registration required

Cons:

Interface feels dated
Ads can be distracting
Mobile experience needs work

Best for: Quick one-off conversions and checking specific city times.

Pricing: Free with ads

3. Datetime.app

We built Datetime.app after getting frustrated with overcomplicated tools. It focuses on instant timezone conversion with a clean, modern interface that works perfectly on all devices.

Pros:

Lightning-fast performance
No ads or signup required
Built-in world clock and calendar
Automatic DST handling
Age calculator and holiday calendar included

Cons:

Newer tool (launched 2024)
Fewer advanced features than some competitors

Best for: Anyone who wants simple, fast timezone conversion without the bloat.

Pricing: Completely free

4. Every Time Zone

Every Time Zone displays all timezones on a single screen with color-coded bands showing business hours, making it perfect for distributed teams.

Pros:

See all zones at once
Color coding for work hours
Clean, minimal design
No setup required

Cons:

No mobile app
Can't save custom zone sets
Limited to current time

Best for: Remote teams needing quick visual reference for global time differences.

Pricing: Free

5. Slack's Built-in Timezone Feature

If your team uses Slack, you already have a solid timezone tool. Hover over any teammate's name to see their local time, or use /timezone commands.

Pros:

Integrated where you work
Automatic team timezone tracking
No extra tools needed
Shows working hours

Cons:

Slack subscription required
Limited to team members
Basic conversion features

Best for: Teams already using Slack for communication.

Pricing: Included with Slack (from $8.75/user/month)

6. Time Zone Converter by 24TimeZones

24TimeZones converter excels at bulk conversions and includes a useful timezone map for visual reference.

Pros:

Convert multiple times at once
Interactive world map
Meeting planner included
Email results feature

Cons:

Heavy advertising
Cluttered interface
Slow loading times

Best for: Occasional users who need visual timezone maps.

Pricing: Free with ads

7. Spacetime (for Developers)

Developers working with timezones in code need Spacetime. This JavaScript library handles timezone math with a simple, intuitive API.

Pros:

Lightweight (35kb)
Immutable and chainable
Handles DST automatically
Great documentation

Cons:

Requires coding knowledge
JavaScript only
Not for end users

Best for: Developers building timezone features into applications.

Pricing: Free (open source)

8. Clockwise

Clockwise uses AI to automatically find the best meeting times across time zones while protecting everyone's focus time. It integrates with Google Calendar and Slack to optimize team schedules.

Pros:

AI-powered scheduling optimization
Protects focus time automatically
Smart meeting suggestions
Slack and Calendar integration
Team analytics dashboard

Cons:

Requires Google Workspace
Learning curve for advanced features
Premium features can be expensive

Best for: Teams that value deep work and want AI-assisted scheduling.

Pricing: Free for individuals, $6.75/user/month for teams

How to Choose the Right Tool

Consider these factors when selecting a timezone converter:

Frequency of use: Daily users need bookmarkable tools or apps
Team size: Larger teams benefit from integrated solutions
Budget: Free tools work fine for most individual needs
Platform: Ensure mobile support if you travel frequently
Privacy: Some tools require calendar access or registration

Final Thoughts

After extensive testing, most people will be perfectly served by free tools like Datetime.app or TimeandDate.com. Teams should consider integrated solutions like Slack's timezone features or Clockwise.

The "best" tool ultimately depends on your specific workflow. I personally use Datetime.app for quick conversions and World Time Buddy for complex scheduling. Try a few options and see what sticks – your future meeting attendees will thank you for getting the time right.

ブログ - 時間管理と生産性の洞察

The 8 Best Timezone Converter Tools in 2025