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Quick Answer
What is Friday − 13 days?
These sentences all describe the same result:
If today is Friday, 13 days before was Saturday
13 days before Friday is Saturday
Friday − 13 days = Saturday
The weekday 13 days before Friday is Saturday
Detailed Math (Step-by-Step)
We show the whole operation clearly (modulo 7).
Step 1: Find the remainder
Since weekdays repeat every 7 days: days mod 7 tells us how many steps to move backward.
| Days | 13 |
|---|---|
| Divide by 7 | 1 remainder 6 |
| Remainder | 6 |
Step 2: Move backward 6 day(s)
Start at Friday and count backward 6 step(s).
| Step | Weekday |
|---|---|
| 0 | Friday (start) |
| 1 | Thursday |
| 2 | Wednesday |
| 3 | Tuesday |
| 4 | Monday |
| 5 | Sunday |
| 6 | Saturday (result) |
Quick Lookup Table
Common values going backward from Friday.
| Days before Friday | Weekday | Remainder (mod 7) |
|---|---|---|
| 0 | Friday | 0 |
| 1 | Thursday | 1 |
| 2 | Wednesday | 2 |
| 3 | Tuesday | 3 |
| 4 | Monday | 4 |
| 5 | Sunday | 5 |
| 6 | Saturday | 6 |
| 7 | Friday | 0 |
| 8 | Thursday | 1 |
| 9 | Wednesday | 2 |
| 10 | Tuesday | 3 |
| 13 | Saturday | 6 |
| 14 | Friday | 0 |
| 21 | Friday | 0 |
| 28 | Friday | 0 |
| 30 | Wednesday | 2 |
Tip: Any number of days that differs by a multiple of 7 lands on the same weekday.
Instant Calculator
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More “Weekday Before” Examples
Check other weekday calculations going backward in time.