Technical / Part 3

Part 3 — Rounding & Daily Values

How computed values become declared values: the 21 CFR 101.9(c) rounding rules, the DV tables, and the exact strings that go on the label.

DBNF-1 · Part 3 Normative Live — exported as BevFacts.round.*

3.1Order of operations

The single most common labeling bug is rounding too early. The normative order is:

compute (Part 2, full precision)
   ├──▶ %DV      = round( unrounded_value / DV × 100 )      // from UNROUNDED values
   └──▶ declared = declaration_round( unrounded_value )      // §3.2, once

%DV is computed from unrounded values, then rounded to a whole percent. Computing %DV from the already-declared mass is nonconforming — it compounds two roundings and can shift the percentage by several points at beverage-typical magnitudes.

3.2Declaration rounding rules

Ties round half-up (2.5 g → 3 g at 1 g increments), matching FDA practice. The functions below are exported verbatim by the reference implementation as BevFacts.round.*.

Quantity	Rule	Function
Calories	< 5 → 0 · ≤ 50 → nearest 5 · > 50 → nearest 10	`round.calories`
Total / sat / trans fat (g)	< 0.5 → 0 · < 5 → nearest 0.5 · ≥ 5 → nearest 1	`round.fat`
Cholesterol (mg)	< 2 → 0 · 2–5 → `"less than 5"` · > 5 → nearest 5	`round.cholesterol`
Sodium (mg)	< 5 → 0 · 5–140 → nearest 5 · > 140 → nearest 10	`round.sodium`
Carb / fiber / sugars / added / protein (g)	< 0.5 → 0 · < 1 → `"less than 1"` · ≥ 1 → nearest 1	`round.gram`
% Daily Value	nearest whole percent (from unrounded mass, §3.1)	—
Caffeine (mg)	< 1 → 0 · 1–5 → `"less than 5"` · > 5 → nearest 5	DBNF rule; no FDA equivalent exists

Note The caffeine rule is DBNF's own: decaf drinks legitimately carry 2–7 mg per shot, and "3 mg" false-precision on a label invites challenges the data can't support. less than 5 communicates "effectively decaf" honestly.

3.3Daily values (2,000 kcal reference diet)

Nutrient	DV	Shown on label?
Total fat	78 g	%DV shown
Saturated fat	20 g	%DV shown
Trans fat	—	mass only, never %DV
Cholesterol	300 mg	%DV shown
Sodium	2,300 mg	%DV shown
Total carbohydrate	275 g	%DV shown
Dietary fiber	28 g	%DV shown
Total sugars	—	mass only, never %DV
Added sugars	50 g	%DV shown — the number DBNF exists for
Protein	50 g	mass only on beverage labels
Caffeine	no DV; 400 mg/day FDA guidance	mass only; guidance %`MAY` appear in companion UI, never on-label

3.4%DV computation

pctDV(nutrient) = round_half_up( unrounded(nutrient) / DV(nutrient) × 100 )   // whole %

Zero declarations still show 0% where the row carries %DV. Values over 100% print as-is (128%) — capping at 100% is nonconforming; the whole point is that one drink can exceed a day.

3.5Declared-string grammar

The exact strings, in ABNF. No locale-dependent formatting inside the value strings; unit is attached without a space, matching FDA convention.

declared-mass  = ( "less than " unit-num / unit-num ) unit
unit-num       = 1*4DIGIT [ "." DIGIT ]        ; "4.5"
unit           = "g" / "mg"
declared-cal   = 1*4DIGIT                       ; no unit on the label
declared-pct   = 1*3DIGIT "%"
added-row      = "Includes " declared-mass " Added Sugars"

Examples: 4.5g · less than 1g · 170mg · Includes 43g Added Sugars · 86%.

3.6Warning thresholds

Warnings are machine-readable flags in the DBNF document (Part 4); companion UIs decide presentation. Thresholds evaluate against unrounded values.

Flag	Condition	UI requirement
`added_sugars_over_50pct_dv`	addedSugars ≥ 25 g	`SHOULD` surface a caution
`added_sugars_over_100pct_dv`	addedSugars ≥ 50 g	`MUST` surface a caution
`caffeine_over_half_daily`	caffeine ≥ 200 mg	`SHOULD` surface
`caffeine_over_daily`	caffeine ≥ 400 mg	`MUST` surface; `SHOULD` require confirmation on kiosks
`clamped_negative`, `energy_reconciliation_failed`	Part 2 §2.7	engine diagnostics; `MUST NOT` be shown to consumers

3.7Test vectors

Verifiable in the console via BevFacts.round.*:

Call	Expected	Why
`round.calories(4.9)`	`0`	< 5 → 0
`round.calories(47.5)`	`50`	≤ 50, nearest 5, half-up
`round.calories(324)`	`320`	> 50, nearest 10
`round.fat(4.74)`	`"4.5"`	< 5, nearest 0.5
`round.fat(5.4)`	`"5"`	≥ 5, nearest 1
`round.cholesterol(3)`	`"less than 5"`	2–5 band
`round.sodium(138)`	`"140"`	5–140, nearest 5
`round.sodium(146)`	`"150"`	> 140, nearest 10
`round.gram(0.7)`	`"less than 1"`	0.5–1 band
`round.gram(0.4)`	`"0"`	< 0.5 → 0