diff --git a/NAMESPACE b/NAMESPACE
index d4c9a14..c2d8638 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -1,6 +1,7 @@
 # Generated by roxygen2: do not edit by hand
 
 export(agg_lt)
+export(agg_tf)
 export(ccmpp)
 export(check_mx_ax_qx)
 export(gen_Tx)
diff --git a/R/00_globals.R b/R/00_globals.R
index 23b5c9f..f326cef 100644
--- a/R/00_globals.R
+++ b/R/00_globals.R
@@ -20,5 +20,5 @@ utils::globalVariables(c("age_int", "age_group_years_start", "age_group_years_en
                          "id_cols_no_age", "sex", "mx_inf", "has_1m0",
                          "new_ax", "max_ax_diff",
                          "year_start", "year_end", "initial_ax",
-                         "prop_female", "srb", "asfr",
+                         "prop_female", "srb", "asfr", "tf",
                          "qx_inf"))
diff --git a/R/agg_tf.R b/R/agg_tf.R
new file mode 100644
index 0000000..93cca26
--- /dev/null
+++ b/R/agg_tf.R
@@ -0,0 +1,114 @@
+#' @title Calculate total fertility aggregates
+#'
+#' @description Calculate total fertility for a specified age range using
+#'   age-specific fertility rates.
+#'
+#' @param dt \[`data.table()`\]\cr
+#'   ASFR input data. Must include all columns in `id_cols`, and a column for
+#'   'asfr'.
+#' @param age_mapping \[`data.table()`\]\cr
+#'  Specification of age interval to aggregate to. Required columns are
+#'  'age_start' and 'age_end'.
+#' @inheritParams hierarchyUtils::agg
+#'
+#' @return \[`data.table()`\]\cr Aggregated total fertility with columns for all
+#'   `id_cols` and a 'tf' column. Will only return the age groups specified in
+#'   `age_mapping`.
+#'
+#' @seealso [hierarchyUtils::agg()]
+#'
+#' @inheritSection hierarchyUtils::agg Severity Arguments
+#'
+#' @details
+#' Calculate total fertility aggregate for ages within a specific age range.
+#' TFR (total fertility rate) is measured over the entire reproductive age span,
+#' typically defined as between age 15 and 49 (or 10 and 54). `agg_tf` also
+#' allows calculation of total fertility for other age spans like total
+#' fertility under 25 and total fertility over 30.
+#'
+#' Total fertility is calculated as the sum of ASFR multiplied by the number of
+#' years in an age group. This number represents the average number of children
+#' born to a woman if (1) she experiences a specific set of age specific
+#' fertility rates and (2) she survives through the end of the age span.
+#' Preston pg 95.
+#'
+#' This is different from an age-specific fertility rate (ASFR) or a crude birth
+#' rate (CBR), both of which are calculated as births/population for a
+#' particular age group or all reproductive ages, respectively.
+#'
+#' @references
+#' Preston, Samuel, Patrick Heuveline, and Michel Guillot. 2001. Demography:
+#' Measuring and Modeling Population. Wiley.
+#'
+#' @examples
+#' # calculate total fertility under 25 (ages 10 to 24)
+#' dt <- data.table::data.table(
+#'   age_start = c(10, 15, 20, 25, 30, 35, 40, 45),
+#'   age_end = c(15, 20, 25, 30, 35, 40, 45, 50),
+#'   asfr = c(0.00005, 0.02, 0.07, 0.08, 0.05, 0.02, 0.004, 0.0002)
+#' )
+#'
+#' dt <- agg_tf(
+#'   dt = dt,
+#'   id_cols = c("age_start", "age_end"),
+#'   age_mapping = data.table::data.table(age_start = 10, age_end = 25)
+#' )
+#'
+#' @export
+agg_tf <- function(dt,
+                   id_cols,
+                   age_mapping,
+                   missing_dt_severity = "stop",
+                   overlapping_dt_severity = "stop",
+                   present_agg_severity = "stop",
+                   na_value_severity = "stop",
+                   quiet = FALSE) {
+
+  # Validate arguments (before `hierarchyUtils::agg`) -----------------------
+
+  # basic checks for 'id_cols` argument
+  assertthat::assert_that(
+    assertive::is_character(id_cols),
+    all(c("age_start", "age_end") %in% id_cols),
+    msg = c("`id_cols` must be a character vector that includes 'age_start',
+            'age_end', & 'asfr'")
+  )
+
+  # basic checks for `dt` argument
+  assertive::assert_is_data.table(dt)
+  assertable::assert_colnames(
+    data = dt, colnames = c(id_cols, "asfr"),
+    only_colnames = F, quiet = T
+  )
+
+  # prep -----------------------------------------------------------------------
+
+  original_col_order <- copy(names(dt))
+  original_keys <- copy(key(dt))
+
+  dt <- copy(dt)
+  hierarchyUtils::gen_length(dt, col_stem = 'age')
+
+  # calculate ------------------------------------------------------------------
+
+  dt <- dt[, tf := asfr * age_length]
+
+  dt <- hierarchyUtils::agg(
+    dt[, .SD, .SDcols = c(id_cols, 'tf')],
+    id_cols = id_cols,
+    value_cols = 'tf',
+    col_stem = 'age',
+    col_type = 'interval',
+    mapping = age_mapping,
+    agg_function = sum,
+    missing_dt_severity = missing_dt_severity,
+    overlapping_dt_severity = overlapping_dt_severity,
+    present_agg_severity = present_agg_severity,
+    na_value_severity = na_value_severity,
+    quiet = quiet
+  )
+
+  data.table::setcolorder(dt, c(setdiff(original_col_order, "asfr"), "tf"))
+  data.table::setkeyv(dt, original_keys)
+  return(dt)
+}
diff --git a/_pkgdown.yml b/_pkgdown.yml
index 44db0a4..2663749 100644
--- a/_pkgdown.yml
+++ b/_pkgdown.yml
@@ -38,6 +38,11 @@ reference:
   - gen_nLx_from_nSx
   - gen_lx_from_nLx_ax
 
+- title: "Fertility metrics"
+  desc: "Functions for calculating fertility related metrics."
+- contents:
+  - agg_tf
+
 - title: "Other"
   desc: "Additional miscellaneous functions."
 - contents:
diff --git a/man/agg_tf.Rd b/man/agg_tf.Rd
new file mode 100644
index 0000000..d10cadc
--- /dev/null
+++ b/man/agg_tf.Rd
@@ -0,0 +1,169 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/agg_tf.R
+\name{agg_tf}
+\alias{agg_tf}
+\title{Calculate total fertility aggregates}
+\usage{
+agg_tf(
+  dt,
+  id_cols,
+  age_mapping,
+  missing_dt_severity = "stop",
+  overlapping_dt_severity = "stop",
+  present_agg_severity = "stop",
+  na_value_severity = "stop",
+  quiet = FALSE
+)
+}
+\arguments{
+\item{dt}{[\code{data.table()}]\cr
+ASFR input data. Must include all columns in \code{id_cols}, and a column for
+'asfr'.}
+
+\item{id_cols}{[\code{character()}]\cr
+ID columns that uniquely identify each row of \code{dt}.}
+
+\item{age_mapping}{[\code{data.table()}]\cr
+Specification of age interval to aggregate to. Required columns are
+'age_start' and 'age_end'.}
+
+\item{missing_dt_severity}{[\code{character(1)}]\cr
+What should happen when \code{dt} is missing levels of \code{col_stem} that
+prevent aggregation or scaling from occurring? Can be either 'skip',
+'stop', 'warning', 'message', or 'none'. Default is 'stop'. See section on
+'Severity Arguments' for more information.}
+
+\item{overlapping_dt_severity}{[\code{character(1)}]\cr
+When aggregating/scaling an interval variable or \code{collapse_interval_cols=TRUE}
+what should happen when overlapping intervals are identified? Can be either
+'skip', 'stop', 'warning', 'message', or 'none'. Default is 'stop'. See
+section on 'Severity Arguments' for more information.}
+
+\item{present_agg_severity}{[\code{logical(1)}]\cr
+What should happen when \code{dt} already has requested aggregates (from
+\code{mapping})? Can be either 'skip', 'stop', 'warning', 'message',
+or 'none'. Default is 'stop'. See section on 'Severity Arguments' for more
+information.}
+
+\item{na_value_severity}{[\code{character(1)}]\cr
+What should happen when 'NA' values are present in \code{value_cols}? Can be
+either 'skip', 'stop', 'warning', 'message', or 'none'. Default is 'stop'.
+See section on 'Severity Arguments' for more information.}
+
+\item{quiet}{[\code{logical(1)}]\cr
+Should progress messages be suppressed as the function is run? Default is
+False.}
+}
+\value{
+[\code{data.table()}]\cr Aggregated total fertility with columns for all
+\code{id_cols} and a 'tf' column. Will only return the age groups specified in
+\code{age_mapping}.
+}
+\description{
+Calculate total fertility for a specified age range using
+age-specific fertility rates.
+}
+\details{
+Calculate total fertility aggregate for ages within a specific age range.
+TFR (total fertility rate) is measured over the entire reproductive age span,
+typically defined as between age 15 and 49 (or 10 and 54). \code{agg_tf} also
+allows calculation of total fertility for other age spans like total
+fertility under 25 and total fertility over 30.
+
+Total fertility is calculated as the sum of ASFR multiplied by the number of
+years in an age group. This number represents the average number of children
+born to a woman if (1) she experiences a specific set of age specific
+fertility rates and (2) she survives through the end of the age span.
+Preston pg 95.
+
+This is different from an age-specific fertility rate (ASFR) or a crude birth
+rate (CBR), both of which are calculated as births/population for a
+particular age group or all reproductive ages, respectively.
+}
+\section{Severity Arguments}{
+
+
+\strong{\code{missing_dt_severity}}:
+
+Check for missing levels of \code{col_stem}, the variable being aggregated or
+scaled over.
+\enumerate{
+\item \code{stop}: throw error (this is the default).
+\item \code{warning} or \code{message}: throw warning/message and continue with
+aggregation/scaling for requested aggregations/scalings where expected input
+data in \code{dt} is available.
+\item \code{none}: don't throw error or warning, continue with aggregation/scaling
+for requested aggregations/scalings where expected input data in \code{dt} is
+available.
+\item \code{skip}: skip this check and continue with aggregation/scaling.
+}
+
+\strong{\code{present_agg_severity}} (\code{agg} only):
+
+Check for requested aggregates in \code{mapping} that are already present
+\enumerate{
+\item \code{stop}: throw error (this is the default).
+\item \code{warning} or \code{message}: throw warning/message, drop aggregates and continue
+with aggregation.
+\item \code{none}: don't throw error or warning, drop aggregates and continue with
+aggregation.
+\item \code{skip}: skip this check and add to the values already present for the
+aggregates.
+}
+
+\strong{\code{na_value_severity}}:
+
+Check for 'NA' values in the \code{value_cols}.
+\enumerate{
+\item \code{stop}: throw error (this is the default).
+\item \code{warning} or \code{message}: throw warning/message, drop missing values and
+continue with aggregation/scaling where possible (this likely will cause
+another error because of \code{missing_dt_severity}, consider setting
+\code{missing_dt_severity = "skip"} for functionality similiar to \code{na.rm = TRUE}).
+\item \code{none}: don't throw error or warning, drop missing values and continue
+with aggregation/scaling where possible (this likely will cause another error
+because of \code{missing_dt_severity}, consider setting
+\code{missing_dt_severity = "skip"} for functionality similiar to \code{na.rm = TRUE}).
+\item \code{skip}: skip this check and propagate \code{NA} values through
+aggregation/scaling.
+}
+
+\strong{\code{overlapping_dt_severity}}:
+Check for overlapping intervals that prevent collapsing to the most detailed
+common set of intervals. Or check for overlapping intervals in \code{col_stem}
+when aggregating/scaling.
+\enumerate{
+\item \code{stop}: throw error (this is the default).
+\item \code{warning} or \code{message}: throw warning/message, drop overlapping intervals
+and continue with aggregation/scaling where possible (this may cause another
+error because of \code{missing_dt_severity}).
+3 \code{none}: don't throw error or warning, drop overlapping intervals and
+continue with aggregation/scaling where possible (this may cause another
+error because of \code{missing_dt_severity}).
+\item \code{skip}: skip this check and continue with aggregation/scaling.
+}
+
+}
+
+\examples{
+# calculate total fertility under 25 (ages 10 to 24)
+dt <- data.table::data.table(
+  age_start = c(10, 15, 20, 25, 30, 35, 40, 45),
+  age_end = c(15, 20, 25, 30, 35, 40, 45, 50),
+  asfr = c(0.00005, 0.02, 0.07, 0.08, 0.05, 0.02, 0.004, 0.0002)
+)
+
+dt <- agg_tf(
+  dt = dt,
+  id_cols = c("age_start", "age_end"),
+  age_mapping = data.table::data.table(age_start = 10, age_end = 25)
+)
+
+}
+\references{
+Preston, Samuel, Patrick Heuveline, and Michel Guillot. 2001. Demography:
+Measuring and Modeling Population. Wiley.
+}
+\seealso{
+\code{\link[hierarchyUtils:agg_scale]{hierarchyUtils::agg()}}
+}
diff --git a/tests/testthat/test_agg_tfr.R b/tests/testthat/test_agg_tfr.R
new file mode 100644
index 0000000..0c98207
--- /dev/null
+++ b/tests/testthat/test_agg_tfr.R
@@ -0,0 +1,37 @@
+library(data.table)
+
+# test dataset from Preston pg 96 Box 5.1
+dt <- data.table::data.table(
+  location = "USA", year = 1992,
+  age_start = seq(10, 45, 5), age_end = seq(15, 50, 5),
+  asfr = c(0.0014, 0.0607, 0.1146, 0.1174, 0.0802, 0.0325, 0.0059, 0.0003)
+)
+
+expected <- data.table::data.table(
+  location = "USA", year = 1992,
+  age_start = 10, age_end = 50,
+  tf = c(2.064)
+)
+
+id_cols <- c("location", "year", "age_start", "age_end")
+mapping <- data.table(age_start = 10, age_end = 50)
+
+test_that("test that `agg_tf` gives expected output", {
+  output_dt <- agg_tf(
+    dt = dt,
+    id_cols = id_cols,
+    age_mapping = mapping
+  )
+  testthat::expect_equivalent(output_dt, expected, tolerance = 1e16)
+})
+
+test_that("test that `agg_tf` gives expected errors", {
+  testthat::expect_error(
+    agg_tf(
+      dt = dt,
+      id_cols = id_cols,
+      age_mapping = data.table(age_start = 10, age_end = 18)
+    ),
+    regexp = "expected input data is missing."
+  )
+})