diff --git a/.stylelintrc b/.stylelintrc
index 50a9473ce34f069058362356f4ac3109bc4a316f..93af80b7de5cbb4474e61012537ce1a50be4cc08 100644
--- a/.stylelintrc
+++ b/.stylelintrc
@@ -10,6 +10,7 @@
       "border-bottom-right-radius",
       "border-bottom-left-radius",
       "transition"
-    ]
+    ],
+    "function-blacklist": ["calc"]
   }
 }
diff --git a/scss/_custom-forms.scss b/scss/_custom-forms.scss
index 8b3a74bc0b6027d3a82c20f33d36d7ff15ef75d2..7df1688fec9c2c29f6e2223e14583e82fecc0bc3 100644
--- a/scss/_custom-forms.scss
+++ b/scss/_custom-forms.scss
@@ -183,8 +183,8 @@
     }
 
     &::after {
-      top: calc(#{(($font-size-base * $line-height-base - $custom-control-indicator-size) / 2)} + #{$custom-control-indicator-border-width * 2});
-      left: calc(#{-($custom-switch-width + $custom-control-gutter)} + #{$custom-control-indicator-border-width * 2});
+      top: add(($font-size-base * $line-height-base - $custom-control-indicator-size) / 2, $custom-control-indicator-border-width * 2);
+      left: add(-($custom-switch-width + $custom-control-gutter), $custom-control-indicator-border-width * 2);
       width: $custom-switch-indicator-size;
       height: $custom-switch-indicator-size;
       background-color: $custom-control-indicator-border-color;
@@ -378,7 +378,7 @@
 
 .custom-range {
   width: 100%;
-  height: calc(#{$custom-range-thumb-height} + #{$custom-range-thumb-focus-box-shadow-width * 2});
+  height: add($custom-range-thumb-height, $custom-range-thumb-focus-box-shadow-width * 2);
   padding: 0; // Need to reset padding
   background-color: transparent;
   appearance: none;
diff --git a/scss/_forms.scss b/scss/_forms.scss
index 7a9a653e4553fae1924cb22006631c392fbc85f6..f91789d656289bb8fcefac54ad6446e7a7e7e7f7 100644
--- a/scss/_forms.scss
+++ b/scss/_forms.scss
@@ -86,23 +86,23 @@ select.form-control {
 // For use with horizontal and inline forms, when you need the label (or legend)
 // text to align with the form controls.
 .col-form-label {
-  padding-top: calc(#{$input-padding-y} + #{$input-border-width});
-  padding-bottom: calc(#{$input-padding-y} + #{$input-border-width});
+  padding-top: add($input-padding-y, $input-border-width);
+  padding-bottom: add($input-padding-y, $input-border-width);
   margin-bottom: 0; // Override the `<label>/<legend>` default
   @include font-size(inherit); // Override the `<legend>` default
   line-height: $input-line-height;
 }
 
 .col-form-label-lg {
-  padding-top: calc(#{$input-padding-y-lg} + #{$input-border-width});
-  padding-bottom: calc(#{$input-padding-y-lg} + #{$input-border-width});
+  padding-top: add($input-padding-y-lg, $input-border-width);
+  padding-bottom: add($input-padding-y-lg, $input-border-width);
   @include font-size($input-font-size-lg);
   line-height: $input-line-height-lg;
 }
 
 .col-form-label-sm {
-  padding-top: calc(#{$input-padding-y-sm} + #{$input-border-width});
-  padding-bottom: calc(#{$input-padding-y-sm} + #{$input-border-width});
+  padding-top: add($input-padding-y-sm, $input-border-width);
+  padding-bottom: add($input-padding-y-sm, $input-border-width);
   @include font-size($input-font-size-sm);
   line-height: $input-line-height-sm;
 }
diff --git a/scss/_functions.scss b/scss/_functions.scss
index 930b7f8972e2fb9f1f5a778a41e4a698378b699f..fc789ac258bcb6e127060db3445f2363f7b52c1e 100644
--- a/scss/_functions.scss
+++ b/scss/_functions.scss
@@ -95,3 +95,40 @@
 
   @return mix($color-base, $color, $level * $theme-color-interval);
 }
+
+// Return valid calc
+@function add($value1, $value2, $return-calc: true) {
+  @if $value1 == null {
+    @return $value2;
+  }
+
+  @if $value2 == null {
+    @return $value1;
+  }
+
+  @if type-of($value1) == number and type-of($value2) == number and comparable($value1, $value2) {
+    @return $value1 + $value2;
+  }
+
+  @return if($return-calc == true, calc(#{$value1} + #{$value2}), #{$value1} + #{$value2});
+}
+
+@function subtract($value1, $value2, $return-calc: true) {
+  @if $value1 == null and $value2 == null {
+    @return null;
+  }
+
+  @if $value1 == null {
+    @return -$value2;
+  }
+
+  @if $value2 == null {
+    @return $value1;
+  }
+
+  @if type-of($value1) == number and type-of($value2) == number and comparable($value1, $value2) {
+    @return $value1 - $value2;
+  }
+
+  @return if($return-calc == true, calc(#{$value1} - #{$value2}), #{$value1} - #{$value2});
+}
diff --git a/scss/_modal.scss b/scss/_modal.scss
index bc08617c95cfa5a1d5720d425306fb804eb9e53d..9a036883a07a1f647b0968fa3aa296694ebfeb6c 100644
--- a/scss/_modal.scss
+++ b/scss/_modal.scss
@@ -52,10 +52,10 @@
 
 .modal-dialog-scrollable {
   display: flex; // IE10/11
-  max-height: calc(100% - #{$modal-dialog-margin * 2});
+  max-height: subtract(100%, $modal-dialog-margin * 2);
 
   .modal-content {
-    max-height: calc(100vh - #{$modal-dialog-margin * 2}); // IE10/11
+    max-height: subtract(100vh, $modal-dialog-margin * 2); // IE10/11
     overflow: hidden;
   }
 
@@ -72,12 +72,12 @@
 .modal-dialog-centered {
   display: flex;
   align-items: center;
-  min-height: calc(100% - #{$modal-dialog-margin * 2});
+  min-height: subtract(100%, $modal-dialog-margin * 2);
 
   // Ensure `modal-dialog-centered` extends the full height of the view (IE10/11)
   &::before {
     display: block; // IE10
-    height: calc(100vh - #{$modal-dialog-margin * 2});
+    height: subtract(100vh, $modal-dialog-margin * 2);
     content: "";
   }
 
@@ -200,18 +200,18 @@
   }
 
   .modal-dialog-scrollable {
-    max-height: calc(100% - #{$modal-dialog-margin-y-sm-up * 2});
+    max-height: subtract(100%, $modal-dialog-margin-y-sm-up * 2);
 
     .modal-content {
-      max-height: calc(100vh - #{$modal-dialog-margin-y-sm-up * 2});
+      max-height: subtract(100vh, $modal-dialog-margin-y-sm-up * 2);
     }
   }
 
   .modal-dialog-centered {
-    min-height: calc(100% - #{$modal-dialog-margin-y-sm-up * 2});
+    min-height: subtract(100%, $modal-dialog-margin-y-sm-up * 2);
 
     &::before {
-      height: calc(100vh - #{$modal-dialog-margin-y-sm-up * 2});
+      height: subtract(100vh, $modal-dialog-margin-y-sm-up * 2);
     }
   }
 
diff --git a/scss/_popover.scss b/scss/_popover.scss
index c9b11e94e89e5b62396f4a8184ea64c893b0032e..0ad76af3eeb6fa6619fcd3a794aaf78b9f61c045 100644
--- a/scss/_popover.scss
+++ b/scss/_popover.scss
@@ -39,7 +39,7 @@
   margin-bottom: $popover-arrow-height;
 
   > .arrow {
-    bottom: calc((#{$popover-arrow-height} + #{$popover-border-width}) * -1);
+    bottom: subtract(-$popover-arrow-height, $popover-border-width);
 
     &::before {
       bottom: 0;
@@ -59,7 +59,7 @@
   margin-left: $popover-arrow-height;
 
   > .arrow {
-    left: calc((#{$popover-arrow-height} + #{$popover-border-width}) * -1);
+    left: subtract(-$popover-arrow-height, $popover-border-width);
     width: $popover-arrow-height;
     height: $popover-arrow-width;
     margin: $popover-border-radius 0; // make sure the arrow does not touch the popover's rounded corners
@@ -82,7 +82,7 @@
   margin-top: $popover-arrow-height;
 
   > .arrow {
-    top: calc((#{$popover-arrow-height} + #{$popover-border-width}) * -1);
+    top: subtract(-$popover-arrow-height, $popover-border-width);
 
     &::before {
       top: 0;
@@ -114,7 +114,7 @@
   margin-right: $popover-arrow-height;
 
   > .arrow {
-    right: calc((#{$popover-arrow-height} + #{$popover-border-width}) * -1);
+    right: subtract(-$popover-arrow-height, $popover-border-width);
     width: $popover-arrow-height;
     height: $popover-arrow-width;
     margin: $popover-border-radius 0; // make sure the arrow does not touch the popover's rounded corners
diff --git a/scss/_variables.scss b/scss/_variables.scss
index be3a0f7985797d69e4ac63eff0f3726c958071d4..eabe960df895c106dcdf0a3394bc80f8624e24a7 100644
--- a/scss/_variables.scss
+++ b/scss/_variables.scss
@@ -495,13 +495,13 @@ $input-plaintext-color:                 $body-color !default;
 
 $input-height-border:                   $input-border-width * 2 !default;
 
-$input-height-inner:                    calc(#{$input-line-height * 1em} + #{$input-padding-y * 2}) !default;
-$input-height-inner-half:               calc(#{$input-line-height * .5em} + #{$input-padding-y}) !default;
-$input-height-inner-quarter:            calc(#{$input-line-height * .25em} + #{$input-padding-y / 2}) !default;
+$input-height-inner:                    add($input-line-height * 1em, $input-padding-y * 2) !default;
+$input-height-inner-half:               add($input-line-height * .5em, $input-padding-y) !default;
+$input-height-inner-quarter:            add($input-line-height * .25em, $input-padding-y / 2) !default;
 
-$input-height:                          calc(#{$input-line-height * 1em} + #{$input-padding-y * 2} + #{$input-height-border}) !default;
-$input-height-sm:                       calc(#{$input-line-height-sm * 1em} + #{$input-btn-padding-y-sm * 2} + #{$input-height-border}) !default;
-$input-height-lg:                       calc(#{$input-line-height-lg * 1em} + #{$input-btn-padding-y-lg * 2} + #{$input-height-border}) !default;
+$input-height:                          add($input-line-height * 1em, add($input-padding-y * 2, $input-height-border, false)) !default;
+$input-height-sm:                       add($input-line-height-sm * 1em, add($input-btn-padding-y-sm * 2, $input-height-border, false)) !default;
+$input-height-lg:                       add($input-line-height-lg * 1em, add($input-btn-padding-y-lg * 2, $input-height-border, false)) !default;
 
 $input-transition:                      border-color .15s ease-in-out, box-shadow .15s ease-in-out !default;
 
@@ -567,7 +567,7 @@ $custom-radio-indicator-icon-checked:           url("data:image/svg+xml,<svg xml
 
 $custom-switch-width:                           $custom-control-indicator-size * 1.75 !default;
 $custom-switch-indicator-border-radius:         $custom-control-indicator-size / 2 !default;
-$custom-switch-indicator-size:                  calc(#{$custom-control-indicator-size} - #{$custom-control-indicator-border-width * 4}) !default;
+$custom-switch-indicator-size:                  subtract($custom-control-indicator-size, $custom-control-indicator-border-width * 4) !default;
 
 $custom-select-padding-y:           $input-padding-y !default;
 $custom-select-padding-x:           $input-padding-x !default;
@@ -586,7 +586,7 @@ $custom-select-indicator-color:     $gray-800 !default;
 $custom-select-indicator:           url("data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg' width='4' height='5' viewBox='0 0 4 5'><path fill='#{$custom-select-indicator-color}' d='M2 0L0 2h4zm0 5L0 3h4z'/></svg>") !default;
 $custom-select-background:          escape-svg($custom-select-indicator) no-repeat right $custom-select-padding-x center / $custom-select-bg-size !default; // Used so we can have multiple background elements (e.g., arrow and feedback icon)
 
-$custom-select-feedback-icon-padding-right: calc((1em + #{2 * $custom-select-padding-y}) * 3 / 4 + #{$custom-select-padding-x + $custom-select-indicator-padding}) !default;
+$custom-select-feedback-icon-padding-right: add(1em * .75, (2 * $custom-select-padding-y * .75) + $custom-select-padding-x + $custom-select-indicator-padding) !default;
 $custom-select-feedback-icon-position:      center right ($custom-select-padding-x + $custom-select-indicator-padding) !default;
 $custom-select-feedback-icon-size:          $input-height-inner-half $input-height-inner-half !default;
 
@@ -766,7 +766,7 @@ $dropdown-bg:                       $white !default;
 $dropdown-border-color:             rgba($black, .15) !default;
 $dropdown-border-radius:            $border-radius !default;
 $dropdown-border-width:             $border-width !default;
-$dropdown-inner-border-radius:      calc(#{$dropdown-border-radius} - #{$dropdown-border-width}) !default;
+$dropdown-inner-border-radius:      subtract($dropdown-border-radius, $dropdown-border-width) !default;
 $dropdown-divider-bg:               $gray-200 !default;
 $dropdown-divider-margin-y:         $nav-divider-margin-y !default;
 $dropdown-box-shadow:               0 .5rem 1rem rgba($black, .175) !default;
@@ -831,7 +831,7 @@ $card-spacer-x:                     1.25rem !default;
 $card-border-width:                 $border-width !default;
 $card-border-radius:                $border-radius !default;
 $card-border-color:                 rgba($black, .125) !default;
-$card-inner-border-radius:          calc(#{$card-border-radius} - #{$card-border-width}) !default;
+$card-inner-border-radius:          subtract($card-border-radius, $card-border-width) !default;
 $card-cap-bg:                       rgba($black, .03) !default;
 $card-cap-color:                    null !default;
 $card-height:                       null !default;
@@ -881,7 +881,7 @@ $popover-max-width:                 276px !default;
 $popover-border-width:              $border-width !default;
 $popover-border-color:              rgba($black, .2) !default;
 $popover-border-radius:             $border-radius-lg !default;
-$popover-inner-border-radius:       calc(#{$popover-border-radius} - #{$popover-border-width}) !default;
+$popover-inner-border-radius:       subtract($popover-border-radius, $popover-border-width) !default;
 $popover-box-shadow:                0 .25rem .5rem rgba($black, .2) !default;
 
 $popover-header-bg:                 darken($popover-bg, 3%) !default;
@@ -953,7 +953,7 @@ $modal-content-bg:                  $white !default;
 $modal-content-border-color:        rgba($black, .2) !default;
 $modal-content-border-width:        $border-width !default;
 $modal-content-border-radius:       $border-radius-lg !default;
-$modal-content-inner-border-radius: calc(#{$modal-content-border-radius} - #{$modal-content-border-width}) !default;
+$modal-content-inner-border-radius: subtract($modal-content-border-radius, $modal-content-border-width) !default;
 $modal-content-box-shadow-xs:       0 .25rem .5rem rgba($black, .5) !default;
 $modal-content-box-shadow-sm-up:    0 .5rem 1rem rgba($black, .5) !default;
 
diff --git a/site/docs/4.3/assets/scss/_sidebar.scss b/site/docs/4.3/assets/scss/_sidebar.scss
index b302b22fea5cc69a436123c38a7bd5ba5fc13cbb..e5e04be746349f4c4b6375bf0ba70c37866da712 100644
--- a/site/docs/4.3/assets/scss/_sidebar.scss
+++ b/site/docs/4.3/assets/scss/_sidebar.scss
@@ -8,7 +8,7 @@
   @supports (position: sticky) {
     position: sticky;
     top: 4rem;
-    height: calc(100vh - 4rem);
+    height: subtract(100vh, 4rem);
     overflow-y: auto;
   }
   order: 2;
@@ -55,7 +55,7 @@
       position: sticky;
       top: 4rem;
       z-index: 1000;
-      height: calc(100vh - 4rem);
+      height: subtract(100vh, 4rem);
     }
     border-right: 1px solid rgba(0, 0, 0, .1);
   }
@@ -73,7 +73,7 @@
 
   @include media-breakpoint-up(md) {
     @supports (position: sticky) {
-      max-height: calc(100vh - 9rem);
+      max-height: subtract(100vh, 9rem);
       overflow-y: auto;
     }
   }
diff --git a/site/docs/4.3/getting-started/theming.md b/site/docs/4.3/getting-started/theming.md
index 198a55da3a61594e473cc4c69d7e22ef3b72e3a7..99c5066c5872997ef88b359724908be85193be7d 100644
--- a/site/docs/4.3/getting-started/theming.md
+++ b/site/docs/4.3/getting-started/theming.md
@@ -227,6 +227,44 @@ You can also specify a base color with our color map functions:
 
 We use the `escape-svg` function to escape the `<`, `>` and `#` characters for SVG background images. These characters need to be escaped to properly render the background images in IE.
 
+## Add and Subtract functions
+
+We use the `add` and `subtract` functions to wrap the CSS `calc` function. The primary purpose of these functions is to avoid errors when a "unitless" `0` value is passed into a `calc` expression. Expressions like `calc(10px - 0)` will return an error in all browsers, despite being mathematically correct.
+
+Example where the calc is valid:
+
+{% highlight scss %}
+$border-radius: .25rem;
+$border-width: 1px;
+
+.element {
+  // Output calc(.25rem - 1px) is valid
+  border-radius: calc($border-radius - $border-width);
+}
+
+.element {
+  // Output the same calc(.25rem - 1px) as above
+  border-radius: subtract($border-radius, $border-width);
+}
+{% endhighlight %}
+
+Example where the calc is invalid:
+
+{% highlight scss %}
+$border-radius: .25rem;
+$border-width: 0;
+
+.element {
+  // Output calc(.25rem - 0) is invalid
+  border-radius: calc($border-radius - $border-width);
+}
+
+.element {
+  // Output .25rem
+  border-radius: subtract($border-radius, $border-width);
+}
+{% endhighlight %}
+
 ## Sass options
 
 Customize Bootstrap 4 with our built-in custom variables file and easily toggle global CSS preferences with new `$enable-*` Sass variables. Override a variable's value and recompile with `npm run test` as needed.