diff --git a/README.md b/README.md
index 37afb36..118edac 100755
--- a/README.md
+++ b/README.md
@@ -56,7 +56,8 @@ Checkout [tests] for more examples.
 
 #### `precision` (default: `5`)
 
-Allow you to define the precision for decimal numbers.
+Allows you to define the precision for decimal numbers. Set it to `false` to
+disable rounding.
 
 ```js
 var out = postcss()
@@ -64,17 +65,6 @@ var out = postcss()
   .process(css).css;
 ```
 
-#### `preserve` (default: `false`)
-
-Allow you to preserve calc() usage in output so browsers will handle decimal
-precision themselves.
-
-```js
-var out = postcss()
-  .use(calc({ preserve: true }))
-  .process(css).css;
-```
-
 #### `warnWhenCannotResolve` (default: `false`)
 
 Adds warnings when calc() are not reduced to a single value.
@@ -87,7 +77,7 @@ var out = postcss()
 
 #### `mediaQueries` (default: `false`)
 
-Allows calc() usage as part of media query declarations.
+Allows calc() usage in media query parameters.
 
 ```js
 var out = postcss()
@@ -95,6 +85,26 @@ var out = postcss()
   .process(css).css;
 ```
 
+Example:
+
+```css
+@media (min-width: calc(100px + 100px)) {
+  div {
+    width: 100px;
+  }
+}
+```
+
+With `mediaQueries: true`, this becomes:
+
+```css
+@media (min-width: 200px) {
+  div {
+    width: 100px;
+  }
+}
+```
+
 #### `selectors` (default: `false`)
 
 Allows calc() usage as part of selectors.
@@ -108,11 +118,13 @@ var out = postcss()
 Example:
 
 ```css
-div[data-size='calc(3*3)'] {
+div:nth-child(calc(1 + 2)) {
   width: 100px;
 }
 ```
 
+With `selectors: true`, this becomes `div:nth-child(3)`.
+
 #### `onParseError`
 
 Callback invoked when a `calc()` body fails to parse or simplify. Matches
diff --git a/src/index.js b/src/index.js
index a5f7e32..01f5576 100644
--- a/src/index.js
+++ b/src/index.js
@@ -25,7 +25,6 @@ const MATCH_CALC = /^(?:-(?:moz|webkit)-)?calc$/i;
 /**
  * @typedef {object} PostCssCalcOptions
  * @property {number | false} [precision]
- * @property {boolean} [preserve]
  * @property {boolean} [warnWhenCannotResolve]
  * @property {boolean} [mediaQueries]
  * @property {boolean} [selectors]
@@ -128,8 +127,7 @@ function transformValue(value, options, result, item) {
 
 /**
  * Runs `transformValue` over one text property of a decl/atrule/rule node
- * and, per `options.preserve`, either updates it in place or inserts a
- * clone carrying the transformed value ahead of the untouched original.
+ * and updates it in place.
  * `setProp` closes over the property name and the concrete node type at
  * each call site, since `Declaration`/`AtRule`/`Rule` don't share a typed
  * "text property" name to index generically.
@@ -142,14 +140,7 @@ function transformValue(value, options, result, item) {
  * @return {void}
  */
 function applyTransform(node, current, setProp, options, result) {
-  const next = transformValue(current, options, result, node);
-  if (options.preserve && current !== next && node.parent) {
-    const clone = node.clone();
-    setProp(clone, next);
-    node.parent.insertBefore(node, clone);
-  } else {
-    setProp(node, next);
-  }
+  setProp(node, transformValue(current, options, result, node));
 }
 
 /**
@@ -160,7 +151,6 @@ function pluginCreator(opts) {
   /** @type {ResolvedOptions} */
   const options = {
     precision: 5,
-    preserve: false,
     warnWhenCannotResolve: false,
     mediaQueries: false,
     selectors: false,
diff --git a/test/index.cjs b/test/index.cjs
index 5a571e6..3ee20ca 100644
--- a/test/index.cjs
+++ b/test/index.cjs
@@ -559,13 +559,6 @@ test(
   )
 );
 
-test(
-  'should preserve the original declaration when `preserve` option is set to true',
-  testCss('foo{bar:calc(1rem * 1.5)}', 'foo{bar:1.5rem;bar:calc(1rem * 1.5)}', {
-    preserve: true,
-  })
-);
-
 test(
   'should not yield warnings when nothing is wrong',
   testValue('calc(500px - 0px)', '500px', { warnWhenCannotResolve: true })
diff --git a/test/unit/plugin.test.mjs b/test/unit/plugin.test.mjs
index 2a2c5e5..3fb79b2 100644
--- a/test/unit/plugin.test.mjs
+++ b/test/unit/plugin.test.mjs
@@ -64,14 +64,10 @@ test('plugin: vendor-prefix wrapper preserved when expression cannot fully resol
   const moz = await process('a{b:-moz-calc(1px + var(--x))}');
   assert.equal(moz.css, 'a{b:-moz-calc(1px + var(--x))}');
 });
-// --- preserve option -----------------------------------------------------
-test('plugin: preserve clones the original decl alongside the simplified one', async () => {
+// --- obsolete JavaScript options ----------------------------------------
+test('plugin: obsolete preserve option is ignored at runtime', async () => {
   const { css } = await process('a{b:calc(1px + 2px)}', { preserve: true });
-  assert.equal(css, 'a{b:3px;b:calc(1px + 2px)}');
-});
-test('plugin: preserve is a no-op when value is unchanged', async () => {
-  const { css } = await process('a{b:red}', { preserve: true });
-  assert.equal(css, 'a{b:red}');
+  assert.equal(css, 'a{b:3px}');
 });
 // --- warnWhenCannotResolve -----------------------------------------------
 test('plugin: warnWhenCannotResolve surfaces unresolved expressions', async () => {
@@ -101,15 +97,12 @@ test('plugin: mediaQueries off leaves @media untouched', async () => {
   );
   assert.match(css, /calc\(100px \+ 100px\)/);
 });
-test('plugin: mediaQueries + preserve clones the @media rule', async () => {
-  // Both options together: the simplified atrule appears, followed by
-  // the original (preserve clones into the parent before the live node).
+test('plugin: mediaQueries transforms the @media rule in place', async () => {
   const { css } = await process(
     '@media (min-width: calc(100px + 100px)) { a{b:c} }',
-    { mediaQueries: true, preserve: true }
+    { mediaQueries: true }
   );
-  assert.match(css, /min-width: 200px/);
-  assert.match(css, /calc\(100px \+ 100px\)/);
+  assert.equal(css, '@media (min-width: 200px) { a{b:c} }');
 });
 // --- onParseError --------------------------------------------------------
 test('plugin: default behavior on parse failure is a PostCSS warn', async () => {
@@ -159,16 +152,12 @@ test('plugin: precision 0 rounds to whole numbers', async () => {
   assert.equal(css, 'a{b:1in}');
 });
 // --- Option combinations -------------------------------------------------
-test('plugin: preserve + warnWhenCannotResolve — both fire together', async () => {
-  // Unresolved expression gets preserved AND warned about.
+test('plugin: obsolete preserve option and warnWhenCannotResolve work together', async () => {
   const { css, warnings } = await process('a{b:calc(100% + var(--x))}', {
     preserve: true,
     warnWhenCannotResolve: true,
   });
-  // preserve clones the original alongside — both have the same
-  // serialized value since the simplifier can't fully reduce this
-  // expression, but the clone step still runs.
-  assert.match(css, /calc\(100% \+ var\(--x\)\)/);
+  assert.equal(css, 'a{b:calc(100% + var(--x))}');
   assert.equal(warnings.length, 1);
 });
 test('plugin: onParseError catches errors in @media params (mediaQueries: true)', async () => {
@@ -189,16 +178,11 @@ test('plugin: selectors:true reduces calc() in selector text', async () => {
   });
   assert.match(css, /:nth-child\(3\)/);
 });
-test('plugin: selectors + preserve clones the rule', async () => {
-  // Same shape as the mediaQueries + preserve case: the simplified rule
-  // appears first, followed by the original (preserve clones into the
-  // parent before the live node).
+test('plugin: selectors transforms the rule in place', async () => {
   const { css } = await process('a:nth-child(calc(1 + 2)) { b: c }', {
     selectors: true,
-    preserve: true,
   });
-  assert.match(css, /:nth-child\(3\)/);
-  assert.match(css, /:nth-child\(calc\(1 \+ 2\)\)/);
+  assert.equal(css, 'a:nth-child(3) { b: c }');
 });
 test('plugin: onParseError does not fire for fully-resolved inputs', async () => {
   const errors = [];
@@ -210,7 +194,6 @@ test('plugin: onParseError does not fire for fully-resolved inputs', async () =>
 test('plugin: options are no-ops on values with no calc()', async () => {
   // Every option branch should harmlessly ignore non-calc declarations.
   const { css, warnings } = await process('a{color:red;padding:10px 20px}', {
-    preserve: true,
     warnWhenCannotResolve: true,
     mediaQueries: true,
     selectors: true,
diff --git a/types/index.d.ts b/types/index.d.ts
index c52f348..6a780b9 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -1,6 +1,5 @@
 export type PostCssCalcOptions = {
     precision?: number | false;
-    preserve?: boolean;
     warnWhenCannotResolve?: boolean;
     mediaQueries?: boolean;
     selectors?: boolean;