| Year to letter | ||||||||
|---|---|---|---|---|---|---|---|---|
| 0 8 16 24 32 40 48 56 64 72 80 88 96 |
1 9 17 25 33 41 49 57 65 73 81 89 97 |
2 10 18 26 34 42 50 58 66 74 82 90 98 |
3 11 19 27 35 43 51 59 67 75 83 91 99 |
4 12 20 28 36 44 52 60 68 76 84 92 |
5 13 21 29 37 45 53 61 69 77 85 93 |
6 14 22 30 38 46 54 62 70 78 86 94 |
7 15 23 31 39 47 55 63 71 79 87 95 |
|
| 1792 - 1799 | bfl | cfl | cfl | cfk | l | cfl | cfl | cfk |
| 1800 - 1807 | bek | bek | bek | bej | aek | bek | bek | bej |
| 1808 - 1815 | aek | bek | bek | bek | bfk | bek | bek | bek |
| 1816 - 1891 | bfk | bek | bek | bek | bfk | bek | bek | bek |
| 1892 - 1899 | cgl | cfl | cfl | cfl | bfl | cfl | cfl | cfl |
| 1900 - 1907 | cfk | bek | bek | bek | bfk | bek | bek | bek |
| 1908 - 1991 | bfk | bek | bek | bek | bfk | bek | bek | bek |
| 1992 - 2003 | cgl | cfl | cfl | cfl | bfl | cfl | cfl | cfl |
| 2004 - 2091 | cgl | cfl | cfl | cfl | cgl | cfl | cfl | cfl |
| 2092 - 2099 | dhm | dgm | dgm | dgm | cgm | dgm | dgm | dgm |
| Beginning of Year | ||||
|---|---|---|---|---|
| Year - 1792 | a | b | c | d |
| January | +9 Niv -21 Plu |
+10 Niv -20 Plu |
+11 Niv -19 Plu |
+12 Niv -18 Plu |
| February | +10 Plu -20 Vnt |
+11 Plu -19 Vnt |
+12 Plu -18 Vnt |
+13 Plu -17 Vnt |
| Middle of Year | ||||
|---|---|---|---|---|
| Year - 1792 | e | f | g | h |
| March | +9 Vnt -21 Ger |
+10 Vnt -20 Ger |
+11 Vnt -19 Ger |
+12 Vnt -18 Ger |
| April | +10 Ger -20 Flo |
+11 Ger -19 Flo |
+12 Ger -18 Flo |
+13 Ger -17 Flo |
| May | +10 Flo -20 Pra |
+11 Flo -19 Pra |
+12 Flo -18 Pra |
+13 Flo -17 Pra |
| June | +11 Pra -19 Mes |
+12 Pra -18 Mes |
+13 Pra -17 Mes |
+14 Pra -16 Mes |
| July | +11 Mes -19 The |
+12 Mes -18 The |
+13 Mes -17 The |
+14 Mes -16 The |
| August | +12 The -18 Fru |
+13 The -17 Fru |
+14 The -16 Fru |
+15 The -15 Fru |
| September | +13 Fru -17 S-C |
+14 Fru -16 S-C |
+15 Fru -15 S-C |
+16 Fru -14 S-C |
| End of Year | ||||
|---|---|---|---|---|
| Year - 1791 | j | k | l | m |
| September | -23 Vnd | -22 Vnd | -21 Vnd | -20 Vnd |
| October | +7 Vnd -23 Bru |
+8 Vnd -22 Bru |
+9 Vnd -21 Bru |
+10 Vnd -20 Bru |
| November | +8 Bru -22 Fri |
+9 Bru -21 Fri |
+10 Bru -20 Fri |
+11 Bru -19 Fri |
| December | +8 Fri -22 Niv |
+9 Fri -21 Niv |
+10 Fri -20 Niv |
+11 Fri -19 Niv |
| Month names and day names | |||||||
|---|---|---|---|---|---|---|---|
| Vnd | Vendémiaire | 1 | 11 | 21 | Primedi / Primidi | ||
| Bru | Brumaire | 2 | 12 | 22 | Duodi | ||
| Fri | Frimaire | 3 | 13 | 23 | Tridi | ||
| Niv | Nivôse | 4 | 14 | 24 | Quartidi | ||
| Plu | Pluviôse | 5 | 15 | 25 | Quintidi | ||
| Vnt | Ventôse | 6 | 16 | 26 | Sextidi | ||
| Ger | Germinal | 7 | 17 | 27 | Septidi | ||
| Flo | Floréal | 8 | 18 | 28 | Octidi | ||
| Pra | Prairial | 9 | 19 | 29 | Nonidi | ||
| Mes | Messidor | 10 | 20 | 30 | Décadi | ||
| The | Thermidor | ||||||
| Fru | Fructidor | ||||||
| S-C | Sans-Culottides / Additional Days | ||||||
Look at the first table. The Gregorian year 1799 belongs to the interval 1792 - 1799 and its last two digits are 99. The cell in the corresponding line and column contains the three letters cfk.
Look at the next three tables. The month November appears in the End of Year table, at the head of which is the fomula Year - 1791. So you can compute that the French Revolutionary year is 8. Of the three letters cfk, the letter k appears in the same table. The corresponding cell contains two formulas: +9 Bru -21 Fri. Choose the one that will convert the day number 09 into a number in the 1-30 range. That is, up to and including 21 November, use the first formula +9 Bru, and later use the second formula -21 Fri. Since the Gregorian day number is 09, you use +9 Bru, and you get 18 Bru. The final step consists in retrieving the day's full name and the month's full name in the last table, which gives Octidi 18 Brumaire VIII.
What about September? The first step is the same, and gives the same three letters cfk.
But September appears both in the Middle of Year table, and in the End of Year table. The first one gives two formulas for the day: +14 Fru and -16 S-C (f column), and one for the year: Year - 1792. The second table gives -22 Vnd for the day (k column) and Year - 1791 for the year.
Try the last formula -22 Vnd, then the prior one -16 S-C, then the first one +14 Fru, until you have a result greater than or equal to 1.
For 09 September 1799, you would choose +14 Fru, with the corresponding year formula Year - 1792, which gives you 23 Fru 0007, or better Tridi 23 Fructidor VII.