Professional Date & Time Calculators

Q: How do I calculate a date 90 days from today for payment terms?

Use our Add/Subtract Days Calculator. Enter today's date, input 90 in the number field, select Add, and click Calculate.

Powerful, accurate, and free tools for project managers, HR professionals, students, and anyone who needs precise date calculations.

Welcome to WeekCalc - Your Complete Date Calculation Suite

In today's fast-paced professional environment, accurate date and time calculations are essential for productivity, project management, compliance, and planning. Whether you're a project manager tracking milestones, an HR professional calculating leave balances, a student planning study schedules, or a business owner managing contracts and deadlines, WeekCalc.com provides the comprehensive suite of free calculators you need.

Our platform offers five specialized calculators, each designed to solve specific date-related challenges that professionals face daily. From determining ISO 8601 week numbers for international business coordination to calculating exact workdays for project timelines, our tools deliver instant, accurate results without requiring spreadsheets, programming knowledge, or expensive software subscriptions.

What sets WeekCalc apart is our commitment to accuracy, speed, and usability. All our calculators are built with vanilla JavaScript for lightning-fast performance, require no downloads or installations, work flawlessly on mobile devices, and respect your privacy by performing all calculations directly in your browser without storing or transmitting your data.

Why Accurate Date Calculations Matter for Your Business

Date calculation errors can have significant consequences in professional settings. A miscalculated project deadline can result in missed opportunities, contractual penalties, or disappointed clients. Incorrect leave balance calculations can lead to payroll errors and employee dissatisfaction. Failing to account for business days versus calendar days can create unrealistic expectations with stakeholders.

According to research from the Project Management Institute, poor time estimation and date management contribute to 37% of project failures. In legal and financial contexts, date precision isn't just important—it's mandatory. Contract terms, statute of limitations periods, interest calculations, and compliance deadlines all depend on exact date arithmetic.

WeekCalc eliminates these risks by providing calculators that follow international standards (like ISO 8601 for week numbering), account for weekends automatically in workday calculations, and present results in multiple formats to suit different professional needs. Our tools have been carefully designed based on feedback from project managers, accountants, HR professionals, and educators who rely on date calculations daily.

Our Complete Calculator Suite

📊Week Number Calculator

Calculate the ISO 8601 week number for any date. Essential for project planning, international business coordination, and manufacturing schedules that use week-based timelines.

📏Days Between Dates

Find the exact number of days, weeks, and months between two dates. Perfect for contract durations, project timelines, age calculations, and event countdown planning.

➕Add/Subtract Days

Calculate future or past dates by adding or subtracting days. Ideal for deadline planning, payment terms (Net 30/60/90), shipment ETAs, and follow-up scheduling.

💼Workday Calculator

Calculate business days excluding weekends. Critical for realistic project scheduling, SLA compliance, delivery estimates, and any timeline that operates on business days only.

🎂Birthday Calculator

Calculate exact age in years, months, and days, plus find your next birthday's day of the week. Useful for age verification, milestone planning, and HR records.

Who Benefits from WeekCalc?

Project Managers & Coordinators

Project managers rely on our Workday Calculator to create realistic timelines that account for actual working days, avoiding the common mistake of using calendar days. Our Week Number Calculator helps coordinate with international teams that reference projects by ISO week numbers, particularly common in European manufacturing and software development sprints.

HR Professionals & People Operations

Human resources teams use our Days Between Dates Calculator to accurately compute employment duration, leave accruals, probation periods, and notice periods. The Birthday Calculator helps verify ages for compliance purposes and plan employee milestone celebrations.

Students & Educators

Students utilize our calculators to plan study schedules, calculate days until exams, and manage assignment deadlines. The Add/Subtract Days Calculator helps them work backward from due dates to create realistic study timelines.

Small Business Owners & Freelancers

Entrepreneurs use WeekCalc to manage payment terms (calculating due dates for "Net 30" invoices), schedule follow-ups, plan product launches, and coordinate with suppliers on delivery schedules that use business days rather than calendar days.

Legal & Compliance Professionals

Legal professionals require exact date calculations for statute of limitations, filing deadlines, contract terms, and compliance periods. Our calculators provide the precision necessary for these critical applications, though we always recommend verification with official systems for legal matters.

Key Features & Benefits

100% Free Forever: No subscriptions, no hidden fees, no feature limitations. All calculators are completely free for unlimited use.
No Registration Required: Start calculating immediately without creating accounts or providing personal information.
Privacy-First Design: All calculations happen in your browser. We don't store, track, or transmit your dates or data.
Mobile-Optimized: Responsive design ensures perfect functionality on smartphones, tablets, and desktops.
Lightning-Fast Performance: Built with vanilla JavaScript for instant results without the bloat of heavy frameworks.
International Standards Compliant: Week numbering follows ISO 8601, ensuring consistency with global business practices.
Accurate Business Day Calculation: Our workday calculator properly excludes weekends for realistic project timelines.
Multiple Output Formats: Results presented in various formats (days, weeks, months) to suit different professional needs.
Educational Content: Each calculator includes comprehensive guides explaining the methodology and best practices.
Accessible Design: Clean interface with clear labels, making calculations intuitive even for first-time users.

Frequently Asked Questions

What is WeekCalc and what calculators do you offer?

WeekCalc is a professional suite of five free date and time calculators: Week Number Calculator (ISO 8601 compliant), Days Between Dates Calculator, Add/Subtract Days Calculator, Workday Calculator (business days only), and Birthday Calculator. All tools are free, require no registration, and work on all devices.

Are the calculators really free? Are there any hidden costs?

Yes, all WeekCalc calculators are 100% free with no hidden costs, subscriptions, or premium tiers. You can use them unlimited times without any restrictions. We support the service through ethical advertising while keeping all features completely free for users.

Do I need to create an account or register to use WeekCalc?

No registration is required. Simply visit any calculator page and start using it immediately. We believe in frictionless access to essential productivity tools, so you can calculate dates without providing any personal information.

How accurate are the date calculations?

Our calculators use JavaScript's built-in Date object and follow international standards like ISO 8601 for week numbering. They account for leap years, month lengths, and weekends automatically. While highly accurate for planning and informational purposes, we recommend verifying critical legal or financial deadlines with official systems.

Do you store or track the dates I enter into the calculators?

No. All calculations are performed entirely in your browser using client-side JavaScript. We do not transmit, store, or have access to any dates or data you enter. Your privacy is completely protected, and your calculations remain confidential.

What is the ISO 8601 week numbering standard?

ISO 8601 is the international standard for date and time representation. In this system, weeks start on Monday, and week 1 of the year is the first week containing a Thursday. This standard is widely used in Europe, manufacturing, project management, and international business for consistent week references.

Why is there a difference between calendar days and business days?

Calendar days include all days of the week (including weekends and holidays), while business days (workdays) typically include only Monday through Friday. This distinction is critical for realistic project planning, SLA agreements, delivery estimates, and payment terms that use business days.

Can I use WeekCalc on my mobile phone or tablet?

Absolutely. WeekCalc is built with mobile-first responsive design, ensuring all calculators work perfectly on smartphones, tablets, and desktop computers. The interface automatically adapts to your screen size for optimal usability.

How do I calculate a date 90 days from today for payment terms?

Use our Add/Subtract Days Calculator. Enter today's date (or your invoice date), input "90" in the number field, select "Add," and click Calculate. The result shows the exact date 90 calendar days forward, perfect for Net 90 payment terms.

Can the Workday Calculator account for public holidays?

The current version excludes weekends (Saturday and Sunday) automatically. Public holidays vary by country and region, so we recommend manually adjusting for holidays specific to your location. A future update may include customizable holiday calendars.

Disclaimer: WeekCalc tools are provided for informational, educational, and planning purposes only. While we strive for accuracy, for critical financial, legal, contractual, or compliance deadlines, always verify dates with official sources, legal counsel, or authoritative systems. For time standards, refer to time.gov.