Epidemiological Week Converter
MMWR (CDC)
ISO 8601
MMWR & ISO Week-to-Date Reference — 2026
Look up the calendar dates for any epidemiological week in 2026. MMWR (CDC) weeks run Sunday to Saturday; ISO 8601 weeks run Monday to Sunday.
| Week | MMWR (Sun–Sat) | ISO (Mon–Sun) |
|---|---|---|
| 1 | Jan 04 – Jan 10 | Dec 29 – Jan 04 |
| 2 | Jan 11 – Jan 17 | Jan 05 – Jan 11 |
| 3 | Jan 18 – Jan 24 | Jan 12 – Jan 18 |
| 4 | Jan 25 – Jan 31 | Jan 19 – Jan 25 |
| 5 | Feb 01 – Feb 07 | Jan 26 – Feb 01 |
| 6 | Feb 08 – Feb 14 | Feb 02 – Feb 08 |
| 7 | Feb 15 – Feb 21 | Feb 09 – Feb 15 |
| 8 | Feb 22 – Feb 28 | Feb 16 – Feb 22 |
| 9 | Mar 01 – Mar 07 | Feb 23 – Mar 01 |
| 10 | Mar 08 – Mar 14 | Mar 02 – Mar 08 |
| 11 | Mar 15 – Mar 21 | Mar 09 – Mar 15 |
| 12 | Mar 22 – Mar 28 | Mar 16 – Mar 22 |
| 13 | Mar 29 – Apr 04 | Mar 23 – Mar 29 |
| 14 | Apr 05 – Apr 11 | Mar 30 – Apr 05 |
| 15 | Apr 12 – Apr 18 | Apr 06 – Apr 12 |
| 16 | Apr 19 – Apr 25 | Apr 13 – Apr 19 |
| 17 | Apr 26 – May 02 | Apr 20 – Apr 26 |
| 18 | May 03 – May 09 | Apr 27 – May 03 |
| 19 | May 10 – May 16 | May 04 – May 10 |
| 20 | May 17 – May 23 | May 11 – May 17 |
| 21 | May 24 – May 30 | May 18 – May 24 |
| 22 | May 31 – Jun 06 | May 25 – May 31 |
| 23 | Jun 07 – Jun 13 | Jun 01 – Jun 07 |
| 24 | Jun 14 – Jun 20 | Jun 08 – Jun 14 |
| 25 | Jun 21 – Jun 27 | Jun 15 – Jun 21 |
| 26 | Jun 28 – Jul 04 | Jun 22 – Jun 28 |
| 27 | Jul 05 – Jul 11 | Jun 29 – Jul 05 |
| 28 | Jul 12 – Jul 18 | Jul 06 – Jul 12 |
| 29 | Jul 19 – Jul 25 | Jul 13 – Jul 19 |
| 30 | Jul 26 – Aug 01 | Jul 20 – Jul 26 |
| 31 | Aug 02 – Aug 08 | Jul 27 – Aug 02 |
| 32 | Aug 09 – Aug 15 | Aug 03 – Aug 09 |
| 33 | Aug 16 – Aug 22 | Aug 10 – Aug 16 |
| 34 | Aug 23 – Aug 29 | Aug 17 – Aug 23 |
| 35 | Aug 30 – Sep 05 | Aug 24 – Aug 30 |
| 36 | Sep 06 – Sep 12 | Aug 31 – Sep 06 |
| 37 | Sep 13 – Sep 19 | Sep 07 – Sep 13 |
| 38 | Sep 20 – Sep 26 | Sep 14 – Sep 20 |
| 39 | Sep 27 – Oct 03 | Sep 21 – Sep 27 |
| 40 | Oct 04 – Oct 10 | Sep 28 – Oct 04 |
| 41 | Oct 11 – Oct 17 | Oct 05 – Oct 11 |
| 42 | Oct 18 – Oct 24 | Oct 12 – Oct 18 |
| 43 | Oct 25 – Oct 31 | Oct 19 – Oct 25 |
| 44 | Nov 01 – Nov 07 | Oct 26 – Nov 01 |
| 45 | Nov 08 – Nov 14 | Nov 02 – Nov 08 |
| 46 | Nov 15 – Nov 21 | Nov 09 – Nov 15 |
| 47 | Nov 22 – Nov 28 | Nov 16 – Nov 22 |
| 48 | Nov 29 – Dec 05 | Nov 23 – Nov 29 |
| 49 | Dec 06 – Dec 12 | Nov 30 – Dec 06 |
| 50 | Dec 13 – Dec 19 | Dec 07 – Dec 13 |
| 51 | Dec 20 – Dec 26 | Dec 14 – Dec 20 |
| 52 | Dec 27 – Jan 02 | Dec 21 – Dec 27 |
| 53 | — | Dec 28 – Jan 03 |
Converting an epi week to calendar dates
An epidemiological week is identified by its number and year, but reporting and analysis often need the actual calendar dates it covers. Enter a week to get its start and end dates, or a date to get its week — in both the CDC (MMWR) and ISO 8601 systems.
Frequently asked questions
How do I convert an MMWR week to a date?
Enter the week number and year in the Week → Date tool above, or find the row in the reference table. Each MMWR week runs from Sunday to Saturday.
What is the difference between MMWR and ISO weeks?
MMWR (CDC) weeks start on Sunday; ISO 8601 weeks start on Monday. The same date can fall in different week numbers under each system.
Can an epidemiological year have 53 weeks?
Yes. Most years have 52 weeks, but some — such as 2020 — have 53. The converter and reference table handle this automatically.