| May 13 | Armenian | Other calendars Armenian 27 Mareri 1475 Aztec Ochpaniztli 3, 7 Ozomahtli Babylonian 25 Nisanu, 2337 SE Balinese pawukon Luang, Pepet, Kajeng, Jaya, Keliwon, Urukung, Buda of Gum… | 1.00 | infobox |
| May 13 | Armenian | 27 Mareri 1475 | 1.00 | infobox |
| May 13 | Aztec | Ochpaniztli 3, 7 Ozomahtli | 1.00 | infobox |
| May 13 | Babylonian | 25 Nisanu, 2337 SE | 1.00 | infobox |
| May 13 | Balinese pawukon | Luang, Pepet, Kajeng, Jaya, Keliwon, Urukung, Buda of Gumbreg, Kala, Dadi, Manuh | 1.00 | infobox |
| May 13 | Bengali | 30 Boisakh, BS 1433 | 1.00 | infobox |
| May 13 | Chinese | Yin Fire Pig・Wall Mansion 27 Sānyuè, Bǐngwǔnián (Lixia, 8 days until Xiaoman) | 1.00 | infobox |
| May 13 | Common Era | 13 May 2026 CE | 1.00 | infobox |
| May 13 | Coptic | 5 Pashons, AM 1742 | 1.00 | infobox |
| May 13 | Egyptian | 27 Thoth, 2775 NE | 1.00 | infobox |
| May 13 | Ethiopian | 5 Genbot, 2018 Amätä Məhrät | 1.00 | infobox |
| May 13 | French Republican | Décade III, Quartidi de Floréal de l'Année 234 de la République | 1.00 | infobox |
| May 13 | Gregorian | 13 May, AD 2026 | 1.00 | infobox |
| May 13 | Hebrew | 26 Iyar, AM 5786 Omer 41 | 1.00 | infobox |
| May 13 | Hindu | 5127 KY・1,872,708・Rāudra Solar: 30 Vaiśākha, 1948 SE Lunisolar: Ekādaśī, Kṛishna pakṣa of Vaiśākha, 2083 VE | 1.00 | infobox |
| May 13 | Icelandic | Miðvikudagur, 21 Harpa 2026 | 1.00 | infobox |
| May 13 | Islamic | 26 Dhu al-Qi'dah, AH 1447 (using tabular method) | 1.00 | infobox |
| May 13 | ISO week date | 2026-W20-3 | 1.00 | infobox |
| May 13 | Japanese | 27 Yayoi, Reiwa 8 (Rikka, 8 days until Shōman) | 1.00 | infobox |
| May 13 | Julian | 30 April, AD 2026 (AM 7534) | 1.00 | infobox |
| May 13 | Julian day | 2461174 | 1.00 | infobox |
| May 13 | Maya | 13.0.13.10.11 4 Zip, 7 Chuen | 1.00 | infobox |
| May 13 | Roman | Pridie Kalendas Maias, MMDCCLXXIX AUC | 1.00 | infobox |
| May 13 | Solar Hijri | 23 Ordibehesht, SH 1405 | 1.00 | infobox |
| May 13 | is a | 133rd day of the year | 0.90 | text |
