diff --git a/packages/ssf/bits/50_date.js b/packages/ssf/bits/50_date.js
index 3c66dba..3627376 100644
--- a/packages/ssf/bits/50_date.js
+++ b/packages/ssf/bits/50_date.js
@@ -55,7 +55,7 @@ function write_date(type/*:number*/, fmt/*:string*/, val, ss0/*:?number*/)/*:str
 		switch(fmt) {
 			case '[h]': case '[hh]': out = val.D*24+val.H; break;
 			case '[m]': case '[mm]': out = (val.D*24+val.H)*60+val.M; break;
-			case '[s]': case '[ss]': out = ((val.D*24+val.H)*60+val.M)*60+Math.round(val.S+val.u); break;
+			case '[s]': case '[ss]': out = ((val.D*24+val.H)*60+val.M)*60+(ss0 < 1 ? Math.round(val.S+val.u) : val.S); break;
 			default: throw 'bad abstime format: ' + fmt;
 		} outl = fmt.length === 3 ? 1 : 2; break;
 		case 101: /* 'e' era */
diff --git a/packages/ssf/bits/82_eval.js b/packages/ssf/bits/82_eval.js
index 9d87f9f..feace2f 100644
--- a/packages/ssf/bits/82_eval.js
+++ b/packages/ssf/bits/82_eval.js
@@ -99,23 +99,14 @@ function eval_fmt(fmt/*:string*/, v/*:any*/, opts/*:any*/, flen/*:number*/) {
 		}
 	}
 	/* time rounding depends on presence of minute / second / usec fields */
-	switch(bt) {
-		case 0: break;
-		case 1:
-			/*::if(!dt) break;*/
-			if(dt.u >= 0.5) { dt.u = 0; ++dt.S; }
-			if(dt.S >=  60) { dt.S = 0; ++dt.M; }
-			if(dt.M >=  60) { dt.M = 0; ++dt.H; }
-			break;
-		case 2:
-			/*::if(!dt) break;*/
-			if(dt.u >= 0.5) { dt.u = 0; ++dt.S; }
-			if(dt.S >=  60) { dt.S = 0; ++dt.M; }
-			break;
+	if (bt > 0 && bt < 3 && dt.u >= 0.5) {
+	 	round_up_date(dt, opts);
 	}
 
 	/* replace fields */
-	var {nstr,out} = replace_fields(out, dt, ss0, v, opts);
+	var replaced = replace_fields(out, dt, ss0, v, opts);
+	var nstr = replaced.nstr;
+	out = replaced.out;
 	var vv = "", myv, ostr;
 	if(nstr.length > 0) {
 		if(nstr.charCodeAt(0) == 40) /* '(' */ {
@@ -183,7 +174,7 @@ function eval_fmt(fmt/*:string*/, v/*:any*/, opts/*:any*/, flen/*:number*/) {
 }
 function replace_fields(fields, dt, ss0, v, opts) {
 	var out = [];
-	for (var i = 0; i < fields.length; i++) {out[i] = {t: fields[i].t, v: fields[i].v}}
+	for (var i = 0; i < fields.length; i++) {out[i] = {t: fields[i].t, v: fields[i].v};}
 	var nstr = "", jj;
 	for(i=0; i < out.length; ++i) {
 		switch(out[i].t) {
diff --git a/packages/ssf/ssf.flow.js b/packages/ssf/ssf.flow.js
index 03d8809..511ac1f 100644
--- a/packages/ssf/ssf.flow.js
+++ b/packages/ssf/ssf.flow.js
@@ -335,7 +335,7 @@ function write_date(type/*:number*/, fmt/*:string*/, val, ss0/*:?number*/)/*:str
 		switch(fmt) {
 			case '[h]': case '[hh]': out = val.D*24+val.H; break;
 			case '[m]': case '[mm]': out = (val.D*24+val.H)*60+val.M; break;
-			case '[s]': case '[ss]': out = ((val.D*24+val.H)*60+val.M)*60+Math.round(val.S+val.u); break;
+			case '[s]': case '[ss]': out = ((val.D*24+val.H)*60+val.M)*60+(ss0 < 1 ? Math.round(val.S+val.u) : val.S); break;
 			default: throw 'bad abstime format: ' + fmt;
 		} outl = fmt.length === 3 ? 1 : 2; break;
 		case 101: /* 'e' era */
@@ -793,23 +793,14 @@ function eval_fmt(fmt/*:string*/, v/*:any*/, opts/*:any*/, flen/*:number*/) {
 		}
 	}
 	/* time rounding depends on presence of minute / second / usec fields */
-	switch(bt) {
-		case 0: break;
-		case 1:
-			/*::if(!dt) break;*/
-			if(dt.u >= 0.5) { dt.u = 0; ++dt.S; }
-			if(dt.S >=  60) { dt.S = 0; ++dt.M; }
-			if(dt.M >=  60) { dt.M = 0; ++dt.H; }
-			break;
-		case 2:
-			/*::if(!dt) break;*/
-			if(dt.u >= 0.5) { dt.u = 0; ++dt.S; }
-			if(dt.S >=  60) { dt.S = 0; ++dt.M; }
-			break;
+	if (bt > 0 && bt < 3 && dt.u >= 0.5) {
+	 	round_up_date(dt, opts);
 	}
 
 	/* replace fields */
-	var {nstr,out} = replace_fields(out, dt, ss0, v, opts);
+	var replaced = replace_fields(out, dt, ss0, v, opts);
+	var nstr = replaced.nstr;
+	out = replaced.out;
 	var vv = "", myv, ostr;
 	if(nstr.length > 0) {
 		if(nstr.charCodeAt(0) == 40) /* '(' */ {
@@ -877,7 +868,7 @@ function eval_fmt(fmt/*:string*/, v/*:any*/, opts/*:any*/, flen/*:number*/) {
 }
 function replace_fields(fields, dt, ss0, v, opts) {
 	var out = [];
-	for (var i = 0; i < fields.length; i++) {out[i] = {t: fields[i].t, v: fields[i].v}}
+	for (var i = 0; i < fields.length; i++) {out[i] = {t: fields[i].t, v: fields[i].v};}
 	var nstr = "", jj;
 	for(i=0; i < out.length; ++i) {
 		switch(out[i].t) {
diff --git a/packages/ssf/ssf.js b/packages/ssf/ssf.js
index 5189668..e35ca57 100644
--- a/packages/ssf/ssf.js
+++ b/packages/ssf/ssf.js
@@ -330,7 +330,7 @@ if(ss0 >= 2) tt = ss0 === 3 ? 1000 : 100;
 		switch(fmt) {
 			case '[h]': case '[hh]': out = val.D*24+val.H; break;
 			case '[m]': case '[mm]': out = (val.D*24+val.H)*60+val.M; break;
-			case '[s]': case '[ss]': out = ((val.D*24+val.H)*60+val.M)*60+Math.round(val.S+val.u); break;
+			case '[s]': case '[ss]': out = ((val.D*24+val.H)*60+val.M)*60+(ss0 < 1 ? Math.round(val.S+val.u) : val.S); break;
 			default: throw 'bad abstime format: ' + fmt;
 		} outl = fmt.length === 3 ? 1 : 2; break;
 		case 101: /* 'e' era */
@@ -786,21 +786,14 @@ function eval_fmt(fmt, v, opts, flen) {
 		}
 	}
 	/* time rounding depends on presence of minute / second / usec fields */
-	switch(bt) {
-		case 0: break;
-		case 1:
-if(dt.u >= 0.5) { dt.u = 0; ++dt.S; }
-			if(dt.S >=  60) { dt.S = 0; ++dt.M; }
-			if(dt.M >=  60) { dt.M = 0; ++dt.H; }
-			break;
-		case 2:
-if(dt.u >= 0.5) { dt.u = 0; ++dt.S; }
-			if(dt.S >=  60) { dt.S = 0; ++dt.M; }
-			break;
+	if (bt > 0 && bt < 3 && dt.u >= 0.5) {
+	 	round_up_date(dt, opts);
 	}
 
 	/* replace fields */
-	var {nstr,out} = replace_fields(out, dt, ss0, v, opts);
+	var replaced = replace_fields(out, dt, ss0, v, opts);
+	var nstr = replaced.nstr;
+	out = replaced.out;
 	var vv = "", myv, ostr;
 	if(nstr.length > 0) {
 		if(nstr.charCodeAt(0) == 40) /* '(' */ {
@@ -868,7 +861,7 @@ if(dt.u >= 0.5) { dt.u = 0; ++dt.S; }
 }
 function replace_fields(fields, dt, ss0, v, opts) {
 	var out = [];
-	for (var i = 0; i < fields.length; i++) {out[i] = {t: fields[i].t, v: fields[i].v}}
+	for (var i = 0; i < fields.length; i++) {out[i] = {t: fields[i].t, v: fields[i].v};}
 	var nstr = "", jj;
 	for(i=0; i < out.length; ++i) {
 		switch(out[i].t) {
diff --git a/packages/ssf/test/date.js b/packages/ssf/test/date.js
index c12c274..5b5aaa3 100644
--- a/packages/ssf/test/date.js
+++ b/packages/ssf/test/date.js
@@ -49,10 +49,34 @@ describe('time format rounding', function() {
   [{date1904: true}, {date1904: false}].forEach(opts => {
     testCases.forEach(testCase => {
       it(testCase.desc + ` (1904: ${opts.date1904})`, 
-        () => testRow([testCase.value, testCase.date1904[`${opts.date1904}`]], headers, opts))
-    })
-  })
-})
+        () => testRow([testCase.value, testCase.date1904[`${opts.date1904}`]], headers, opts));
+    });
+  });
+});
+
+describe('time format precision rounding', function() {
+  var value = "4018.99999998843";
+  var testCases = [
+    {desc: "end-of-year thousandths rounding", format: "mm/dd/yyyy hh:mm:ss.000", expected: "12/31/1910 23:59:59.999"},
+    {desc: "end-of-year hundredths round up", format: "mm/dd/yyyy hh:mm:ss.00", expected: "01/01/1911 00:00:00.00"},
+    {desc: "end-of-year minutes round up", format: "mm/dd/yyyy hh:mm", expected: "01/01/1911 00:00"},
+    {desc: "hour duration thousandths rounding", format: "[hh]:mm:ss.000", expected: "96455:59:59.999"},
+    {desc: "hour duration hundredths round up", format: "[hh]:mm:ss.00", expected: "96456:00:00.00"},
+    {desc: "hour duration minute round up (w/ ss)", format: "[hh]:mm:ss", expected: "96456:00:00"},
+    {desc: "hour duration minute round up", format: "[hh]:mm", expected: "96456:00"},
+    {desc: "hour duration round up", format: "[hh]", expected: "96456"},
+    {desc: "minute duration thousandths rounding", format: "[mm]:ss.000", expected: "5787359:59.999"},
+    {desc: "minute duration hundredths round up", format: "[mm]:ss.00", expected: "5787360:00.00"},
+    {desc: "minute duration round up", format: "[mm]:ss", expected: "5787360:00"},
+    {desc: "second duration thousandths rounding", format: "[ss].000", expected: "347241599.999"},
+    {desc: "second duration hundredths round up", format: "[ss].00", expected: "347241600.00"},
+    {desc: "second duration round up", format: "[ss]", expected: "347241600"},
+  ];
+  testCases.forEach(testCase => {
+    var headers = ["value", testCase.format];
+    it(testCase.desc, () => {testRow([value, testCase.expected], headers, {})});
+  });
+});
  
 describe('date formats', function() {
   doit(process.env.MINTEST ? dates.slice(0,4000) : dates);