Can I use it for twins?

No. Multiple pregnancies are not implemented, and the singleton formula must not be extrapolated.

Why does it use pre-pregnancy BMI?

CDC/IOM singleton total and later-week ranges differ by the BMI category before pregnancy.

Why is the week-8 range the same as week 13?

Guidance provides a whole first-trimester range rather than a linear weekly trajectory, so the calculator does not invent one.

Does being outside the range mean something is wrong?

Not by itself. Weight includes fluid and other changes, and clinical interpretation requires pregnancy history and examination.

Why stop at 40 weeks?

The implemented trajectory is bounded to the standard 0–40-week display and does not extrapolate guidance beyond it.

Singleton Pregnancy Weight Reference

See how CDC/IOM guidance relates to pre-pregnancy BMI and week—with medical limits kept explicit.

CDC/IOM singleton ranges

Metric or imperial

No multiple-pregnancy extrapolation

Unit system

Metric (kg, cm)Imperial (lb, in)

Pre-pregnancy weightEnter kilograms in metric mode (30–300 kg) or pounds in imperial mode (66–660 lb).HeightEnter centimeters in metric mode (120–250 cm) or inches in imperial mode (48–98 in).Completed gestational weekWhole weeks from 0 through 40. The formula is not extended past week 40.

How to View the Guideline Range

This educational tool needs pre-pregnancy measurements because CDC categories are based on BMI before pregnancy.

Select metric or imperial units.

The first trimester is not linear

For weeks 1–13, the calculator shows the published whole-trimester 1.1–4.4 lb (0.5–2.0 kg) reference and does not invent a week-specific trajectory.

BMI-Based Singleton Guidance

CDC lists total singleton gain ranges of 28–40 lb for pre-pregnancy BMI below 18.5, 25–35 lb for BMI 18.5–24.9, 15–25 lb for BMI 25.0–29.9, and 11–20 lb for BMI 30 or above. After week 13, this implementation combines the first-trimester range with published category-specific weekly ranges.

Pregnancy Reference Examples

Normal-BMI example at week 20

Pre-pregnancy measurements and week

prepregnancyWeight:140

height:65

gestationalWeek:20

units:imperial

Educational range

6.7–11.4 lb cumulative reference gain

Seven completed weeks after week 13 use 0.8–1.0 lb/week plus the 1.1–4.4 lb first-trimester range.

First-trimester display

Pre-pregnancy measurements and week

prepregnancyWeight:65

height:170

gestationalWeek:8

units:metric

Educational range

0.5–2.0 kg for the whole first trimester

The result is deliberately not divided into a week-eight target.

Clinical context comes first

A number outside a displayed range cannot determine whether a pregnancy is healthy.

Frequently Asked Questions

No. It is an educational display of general singleton guidance. Your prenatal professional should set and interpret individualized goals.

Still have questions about this calculation?

Try the Calculator

CDC/IOM Singleton Formula

Pre-pregnancy BMI determines one of four adult singleton categories.

Metric:BMI = weight kg / height m²

Imperial:For imperial units: reference gain = 1.1–4.4 lb (0.5–2.0 kg) for the whole trimester

Formula

BMI = weight kg / height m²

Pre-pregnancy BMI

BMI = weight kg / height m²

Weeks 1–13

reference gain = 1.1–4.4 lb (0.5–2.0 kg) for the whole trimester

Weeks 14–40

cumulative range = first-trimester range + (week − 13) × category weekly range

Scientific Background

CDC presents recommendations derived from Institute of Medicine guidance for women pregnant with one baby. This implementation intentionally excludes twin and higher-order pregnancy calculations.