diff --git a/draftlogs/7900_fix.md b/draftlogs/7900_fix.md
new file mode 100644
index 00000000000..bee5d62ee9e
--- /dev/null
+++ b/draftlogs/7900_fix.md
@@ -0,0 +1 @@
+- Fix `hovertemplate`/`texttemplate`/`tickformat`/`hoverformat` improperly handling d3-format specs that start with a sign flag such as `+.2f` [[#7900](https://github.com/plotly/plotly.js/pull/7900)]
diff --git a/src/lib/index.js b/src/lib/index.js
index d898a526140..ec1cf71b51e 100644
--- a/src/lib/index.js
+++ b/src/lib/index.js
@@ -19,8 +19,16 @@ lib.adjustFormat = function adjustFormat(formatStr) {
     if (/^\d%/.test(formatStr)) return '~%';
     if (/^\ds/.test(formatStr)) return '~s';
 
-    // try adding tilde to the start of format in order to trim
-    if (!/^[~,.0$]/.test(formatStr) && /[&fps]/.test(formatStr)) return '~' + formatStr;
+    // A d3-format spec may begin with a sign flag (+, -, (, space). Look past
+    // that prefix before deciding whether to trim, and reattach it: prepending
+    // the tilde to the whole string (e.g. "~+.2f") is an invalid spec that
+    // d3Format rejects, so "+.2f" used to be silently dropped.
+    var prefix = (formatStr.match(/^[+\-( ]/) || [''])[0];
+    var rest = formatStr.slice(prefix.length);
+
+    // try adding tilde to trim trailing zeros; leave symbol-led specs ($, #)
+    // untrimmed, since the symbol isn't part of the prefix we stripped above
+    if (!/^[~,.0$#]/.test(rest) && /[&fps]/.test(rest)) return prefix + '~' + rest;
 
     return formatStr;
 };
diff --git a/test/jasmine/tests/lib_number_format_test.js b/test/jasmine/tests/lib_number_format_test.js
index 21ddad84809..e0c40479f2b 100644
--- a/test/jasmine/tests/lib_number_format_test.js
+++ b/test/jasmine/tests/lib_number_format_test.js
@@ -53,6 +53,17 @@ describe('number format', function() {
         { format: '0f', number: float, exp: '12345.678901'},
         { format: '1f', number: float, exp: '12345.678901'},
 
+        // sign flag with an explicit precision must not be dropped (was silently
+        // ignored because adjustFormat produced the invalid spec "~+.2f")
+        { format: '+.2f', number: float, exp: '+12345.68'},
+        { format: '+.0f', number: float, exp: '+12346'},
+        { format: '-.4f', number: float, exp: '12345.6789'},
+
+        // symbol-led specs ($, #) are left untrimmed
+        { format: '$f', number: 1.5, exp: '$1.500000'},
+        { format: '#f', number: 1.5, exp: '1.500000'},
+        { format: '$s', number: 1500, exp: '$1.50000k'},
+
         // space-filled and default sign
         { format: '-13', number: float, exp: '-12345.678901'},
         { format: '-14', number: float, exp: ' -12345.678901'},