📅 Date Calculator — Add Days, Date Diff & Age

Add or subtract days from any date, calculate the difference between two dates, and compute age from a birthdate. Three calculators in one free online date tool.

Start Date

Days

Operation

How to Use

Choose a calculator tab

Select Add/Subtract to offset a date, Date Difference to find the gap between two dates, or Age to compute exact age from a birthdate.

Enter your dates

Use the native date picker or type in YYYY-MM-DD format. All calculations update instantly as you change the inputs.

Read the result

Results show in multiple units simultaneously — days, weeks, months, and years — so you can use whichever suits your needs.

Frequently Asked Questions

How do I calculate days between two dates? +

Switch to the Date Difference tab, enter a start and end date, and the result shows instantly in days, weeks, months, and years.

Can I add business days instead of calendar days? +

The current version uses calendar days. A business-days option (skipping weekends and holidays) is planned for a future update.

How accurate is the age calculator? +

Very accurate — it accounts for leap years and calculates your exact age in years, months, and days as of today.

What date range does it support? +

Any date from the year 0001 to 9999. The native browser date picker handles input validation.

Guide : Calculateur de Dates

Qu'est-ce que c'est ?

Le Calculateur de Dates effectue des calculs sur les dates : différence entre deux dates, ajout/soustraction de jours/mois/années, et conversion entre fuseaux horaires.

Utile pour les délais de projet, les calculs d'âge, les dates d'expiration et les planifications d'événements.

Comment utiliser

Sélectionnez le type de calcul : différence, addition ou soustraction.
Entrez la ou les dates cibles.
Spécifiez l'unité (jours, mois, années ou semaines).
Le résultat s'affiche instantanément.

Conseils professionnels

Attention aux années bissextiles et aux changements d'heure lors des calculs de dates précis.
Stockez toujours les dates en UTC dans les bases de données pour éviter les bugs de fuseau horaire.