Date Add / Subtract Calculator
About Month Number Calculator
The Month Number, Name & Calendar Position Converter translates month numbers ($1-12$) to English/International month names, 3-letter abbreviations (Jan-Dec), Roman numerals (I-XII), quarterly assignments (Q1-Q4), and total days per month ($28, 29, 30, 31$).
How to Use Month Number Calculator
Step 1
Type a month number ($1-12$) or select a month name.
Step 2
Review computed month metadata, quarter assignment, and day counts.
Step 3
Click "Copy Month Details".
Practical Use Cases for Month Number Calculator
Software Developer 0-Indexed vs. 1-Indexed Month Mapping
Convert between human 1-indexed months (January = 1) and JavaScript/POSIX 0-indexed months (January = 0) to avoid off-by-one date bugs.
Accounting Financial Month & Fiscal Period Mapping
Map calendar month numbers to corporate fiscal periods (Period 1 to Period 12) for general ledger entries.
Input & Output Examples
Converting Month Number 8 (August)
Month: `8` (or `August`)
Name: `August` | Short: `Aug` | Roman: `VIII` | Quarter: `Q3` | 0-Index (JS): `7` | Days: `31 days` | Season: `Summer`
Key Features & Performance
- ✓Bi-Directional Converter: input month number, English name, or abbreviation for instant full metadata.
- ✓Developer Index Helper: shows 1-indexed ($1-12$), 0-indexed ($0-11$), and ISO-8601 two-digit format (`01-12`).
- ✓Leap Year Toggle: shows February days in common year (28) vs. leap year (29).
- ✓100% Client-Side memory execution.
- ✓1-Click Copy month specifications.
Key Terminology & Definitions
0-Indexed Month
The programming convention used by JavaScript (`Date.getMonth()`), Python `struct_time`, and C where January is represented as 0 and December as 11.
Quarterly Allocation
The division of the 12 calendar months into four consecutive 3-month business quarters (Q1: Jan-Mar, Q2: Apr-Jun, Q3: Jul-Sep, Q4: Oct-Dec).