diff --git a/R/build.R b/R/build.R
index 7b7c74d..36d094e 100644
--- a/R/build.R
+++ b/R/build.R
@@ -75,6 +75,10 @@ build.ardis <- function(x, layer=NULL, where=TRUE, ...) {
   # If the pre-build wasn't executed then execute it
   if (!'built_target' %in% ls(x)) {
     treatment_group_build(x)
+  }
+
+  # If header N's haven't been supplied, then construct them
+  if (!"header_n" %in% ls(x)) {
     x <- build_header_n(x)
   }
 
diff --git a/R/count.R b/R/count.R
index afbc557..3f117be 100644
--- a/R/count.R
+++ b/R/count.R
@@ -402,15 +402,31 @@ process_count_denoms <- function(x) {
         ) %>%
       ungroup()
 
-    denoms_df_dist <- built_pop_data %>%
-      filter(!!denom_where) %>%
-      group_by(!!pop_treat_var) %>%
-      summarize(
-        distinct_n = n_distinct(!!!distinct_by, !!pop_treat_var)
-      ) %>%
-      ungroup()
+    # Use cached header N's if they're available
+    if (exists("cached_header_n")) {
+      denoms_df_dist <- header_n %>%
+        rename(distinct_n = n)
+
+      # If there was a treatment variable remap provided, add it
+      if (!quo_is_null(header_treat_var)) {
+        by_join <- as_name(header_treat_var)
+      }
+      else {
+        by_join <- as_name(pop_treat_var)
+      }
+    } else {
+      # Calculate header N's from pop data if it wasn't available
+      denoms_df_dist <- built_pop_data %>%
+        filter(!!denom_where) %>%
+        group_by(!!pop_treat_var) %>%
+        summarize(
+          distinct_n = n_distinct(!!!distinct_by, !!pop_treat_var)
+        ) %>%
+        ungroup()
+
+      by_join <- as_name(pop_treat_var)
+    }
 
-    by_join <- as_name(pop_treat_var)
     names(by_join) <- as_name(treat_var)
 
     denoms_df <- denoms_df_n %>%
diff --git a/R/table_bindings.R b/R/table_bindings.R
index db1d54e..6e595b4 100644
--- a/R/table_bindings.R
+++ b/R/table_bindings.R
@@ -19,7 +19,7 @@
 #' @param table A \code{ardis} object
 #'
 #' @return For \code{ardis_header_n} the header_n binding of the
-#'   \code{ardis} object. For \code{ardis_header_n<-} and
+#'   \code{ardis} object. For \code{header_n<-} and
 #'   \code{set_ardis_header_n} the modified object.
 #'
 #' @examples
@@ -38,31 +38,32 @@ header_n <- function(table) {
   env_get(table, "header_n")
 }
 
-#' @param x A \code{ardis} object
-#' @param value A data.frame with columns with the treatment variable, column
+#' @param table A \code{ardis} object
+#' @param x A data.frame with columns with the treatment variable, column
 #'   variabes, and a variable with counts named 'n'.
 #'
 #' @export
 #' @rdname header_n
-`header_n<-` <- function(x, value) {
-  set_header_n(x, value)
+`header_n<-` <- function(table, x) {
+  set_header_n(table, x)
 }
 
-#' @param header_n A data.frame with columns with the treatment variable, column
-#'   variabes, and a variable with counts named 'n'.
+#' @param header_treat_var The symbol name of the treatment variable in the header_n data frame. Provide unquoted
 #'
 #' @export
 #' @rdname header_n
-set_header_n <- function(table, value) {
-  assert_that(is.data.frame(value),
+set_header_n <- function(table, x, header_treat_var = NULL) {
+  header_treat_var <- enquo(header_treat_var)
+
+  assert_that(is.data.frame(x),
                           msg = "header_n argument must be numeric")
 
-  assert_that("n" %in% names(value))
+  assert_that("n" %in% names(x))
 
-  assert_that(is.numeric(value$n),
+  assert_that(is.numeric(x$n),
               msg = "header_n argument must be named")
 
-  env_bind(table, header_n = value)
+  env_bind(table, header_n = x, header_treat_var = header_treat_var, cached_header_n = TRUE)
 
   table
 }
@@ -194,9 +195,13 @@ pop_treat_var <- function(table) {
 set_pop_treat_var <- function(table, pop_treat_var) {
   pop_treat_var <- enquo(pop_treat_var)
 
-  assert_that(class(quo_get_expr(pop_treat_var)) == "name",
-                          as_name(quo_get_expr(pop_treat_var)) %in% names(table$pop_data),
-                          msg = paste0("pop_treat_var passed to ardis is not a column of pop_data"))
+  if (!exists("cached_header_n", envir=table)) {
+    assert_that(class(quo_get_expr(pop_treat_var)) == "name",
+                as_name(quo_get_expr(pop_treat_var)) %in% names(table$pop_data),
+                msg = paste0("pop_treat_var passed to ardis is not a column of pop_data. ",
+                             "Did you forget to use `set_pop_data()` or `set_header_n()` ",
+                             "before calling `set_pop_treat_var()`?"))
+  }
 
   env_bind(table, pop_treat_var = pop_treat_var)
 
diff --git a/man/header_n.Rd b/man/header_n.Rd
index b49ee24..8eb444a 100644
--- a/man/header_n.Rd
+++ b/man/header_n.Rd
@@ -8,24 +8,21 @@
 \usage{
 header_n(table)
 
-header_n(x) <- value
+header_n(table, x) <- value
 
-set_header_n(table, value)
+set_header_n(table, x, header_treat_var = NULL)
 }
 \arguments{
 \item{table}{A \code{ardis} object}
 
-\item{x}{A \code{ardis} object}
-
-\item{value}{A data.frame with columns with the treatment variable, column
+\item{x}{A data.frame with columns with the treatment variable, column
 variabes, and a variable with counts named 'n'.}
 
-\item{header_n}{A data.frame with columns with the treatment variable, column
-variabes, and a variable with counts named 'n'.}
+\item{header_treat_var}{The symbol name of the treatment variable in the header_n data frame. Provide unquoted}
 }
 \value{
 For \code{ardis_header_n} the header_n binding of the
-  \code{ardis} object. For \code{ardis_header_n<-} and
+  \code{ardis} object. For \code{header_n<-} and
   \code{set_ardis_header_n} the modified object.
 }
 \description{