Index: src/date.c
==================================================================
--- src/date.c
+++ src/date.c
@@ -628,16 +628,18 @@
   u8 nName;           /* Length of the name */
   char zName[7];      /* Name of the transformation */
   float rLimit;       /* Maximum NNN value for this transform */
   float rXform;       /* Constant used for this transform */
 } aXformType[] = {
-  { 6, "second", 4.6427e+14,       1.0  },
-  { 6, "minute", 7.7379e+12,      60.0  },
-  { 4, "hour",   1.2897e+11,    3600.0  },
-  { 3, "day",    5373485.0,    86400.0  },
-  { 5, "month",  176546.0,   2592000.0  },
-  { 4, "year",   14713.0,   31536000.0  },
+  /* 0 */ { 6, "second",   4.6427e+14,         1.0  },
+  /* 1 */ { 6, "minute",   7.7379e+12,        60.0  },
+  /* 2 */ { 4, "hour",     1.2897e+11,      3600.0  },
+  /* 3 */ { 3, "day",      5373485.0,      86400.0  },
+  /* 4 */ { 5, "month",    176546.0,  30.0*86400.0  },
+  /* 5 */ { 4, "mnth",     176546.0,  30.0*86400.0  },
+  /* 6 */ { 4, "year",     14713.0,  365.0*86400.0  },
+  /* 7 */ { 2, "yr",       14713.0,  365.0*86400.0  },
 };
 
 /*
 ** If the DateTime p is raw number, try to figure out if it is
 ** a julian day number of a unix timestamp.  Set the p value
@@ -954,43 +956,58 @@
       /* If control reaches this point, it means the transformation is
       ** one of the forms like "+NNN days".  */
       z += n;
       while( sqlite3Isspace(*z) ) z++;
       n = sqlite3Strlen30(z);
-      if( n>10 || n<3 ) break;
+      if( n>10 || n<2 ) break;
       if( sqlite3UpperToLower[(u8)z[n-1]]=='s' ) n--;
       computeJD(p);
       assert( rc==1 );
       rRounder = r<0 ? -0.5 : +0.5;
       for(i=0; i<ArraySize(aXformType); i++){
         if( aXformType[i].nName==n
          && sqlite3_strnicmp(aXformType[i].zName, z, n)==0
          && r>-aXformType[i].rLimit && r<aXformType[i].rLimit
         ){
+          int targetMonth = 0;
           switch( i ){
-            case 4: { /* Special processing to add months */
-              assert( strcmp(aXformType[i].zName,"month")==0 );
+            case 4:
+            case 5: { /* Special processing to add months */
+              assert( strcmp(aXformType[4].zName,"month")==0 );
+              assert( strcmp(aXformType[5].zName,"mnth")==0 );
               computeYMD_HMS(p);
               p->M += (int)r;
               x = p->M>0 ? (p->M-1)/12 : (p->M-12)/12;
               p->Y += x;
               p->M -= x*12;
+              assert( p->M>=1 && p->M<=12 );
+              if( i==5 ) targetMonth = p->M;
               p->validJD = 0;
               r -= (int)r;
               break;
             }
-            case 5: { /* Special processing to add years */
+            case 6:
+            case 7: { /* Special processing to add years */
               int y = (int)r;
-              assert( strcmp(aXformType[i].zName,"year")==0 );
+              assert( strcmp(aXformType[6].zName,"year")==0 );
+              assert( strcmp(aXformType[7].zName,"yr")==0 );
               computeYMD_HMS(p);
+              assert( p->M>=1 && p->M<=12 );
+              if( i==7 ) targetMonth = p->M;
               p->Y += y;
               p->validJD = 0;
               r -= (int)r;
               break;
             }
           }
           computeJD(p);
+          if( targetMonth>0 ){
+            p->validYMD = 0;
+            computeYMD(p);
+            if( p->M==targetMonth+1 ) p->iJD -= p->D*86400000;
+            p->validYMD = 0;
+          }
           p->iJD += (sqlite3_int64)(r*1000.0*aXformType[i].rXform + rRounder);
           rc = 0;
           break;
         }
       }

Index: test/date.test
==================================================================
--- test/date.test
+++ test/date.test
@@ -145,10 +145,19 @@
 datetest 2.49 {datetime('2003-10-22 12:24','0000 second')} {2003-10-22 12:24:00}
 datetest 2.50 {datetime('2003-10-22 12:24','0001 second')} {2003-10-22 12:24:01}
 datetest 2.51 {datetime('2003-10-22 12:24','nonsense')} NULL
 
 datetest 2.60 {datetime('2023-02-31')} {2023-03-03 00:00:00}
+
+datetest 2.70 {date('2024-01-31','+1 month')} {2024-03-02}
+datetest 2.71 {date('2024-01-31','+1 mnth')} {2024-02-29}
+datetest 2.72 {date('2023-01-31','+1 month')} {2023-03-03}
+datetest 2.73 {date('2023-01-31','+1 mnth')} {2023-02-28}
+datetest 2.74 {date('2024-02-29','+1 year')} {2025-03-01}
+datetest 2.75 {date('2024-02-29','+1 yr')} {2025-02-28}
+datetest 2.76 {date('2024-02-29','-110 years')} {1914-03-01}
+datetest 2.77 {date('2024-02-29','-110 yrs')} {1914-02-28}
 
 datetest 3.1 {strftime('%d','2003-10-31 12:34:56.432')} 31
 datetest 3.2.1 {strftime('pre%fpost','2003-10-31 12:34:56.432')} pre56.432post
 datetest 3.2.2 {strftime('%f','2003-10-31 12:34:59.9999999')} 59.999
 datetest 3.3 {strftime('%H','2003-10-31 12:34:56.432')} 12