Most people use a BMI calculator to answer "where do I stand today?" But there's a second, less obvious question worth asking: "what weight, at my height, would put me at the BMI I actually want?" That's reverse BMI — and it turns a screening number into a concrete, trackable goal.
What is reverse BMI, and why bother with it?
Quick answerReverse BMI flips the usual calculation: instead of plugging in your current weight to get a BMI, you plug in a target BMI and your height to get the weight that would produce it. The formula is simply the standard one rearranged: weight (lb) = target BMI × height (in)² ÷ 703.
The regular BMI calculation is diagnostic — it tells you where you are right now. Reverse BMI is prescriptive — it tells you where a specific number on the scale would land you. That distinction matters for goal-setting: "lose weight" is vague, but "reach 152 lb, which puts me at a BMI of 23.8" is a number you can watch trend toward on a bathroom scale every week.
This isn't a new formula or a different health metric — it's the same CDC/WHO BMI math, just solved for a different variable. If you've ever seen a "what should I weigh?" quick-answer field next to a BMI tool, that's exactly what it's doing under the hood.
How do you choose a target BMI in the first place?
Quick answerMost people aim somewhere inside the CDC/WHO normal range of 18.5–24.9, often nearer the middle (roughly 21–23) rather than right at either edge — both boundaries are category cutoffs, not proven optimal points for any one individual.
It's tempting to just pick 24.9 because it's "still normal," or 18.5 because it's the lowest normal number, but treating either boundary as a finish line misses the point of the range: it's a band, not a target. Two reasonable starting approaches:
- Midpoint approach — pick something near the center of the normal range (around 21.5–22.5) as a general-purpose target, adjusting for personal factors like frame size or athletic build.
- Incremental approach — if the current BMI is well outside the normal range, set an intermediate target (say, moving from a BMI of 31 toward 27 first) rather than jumping straight to 22, which keeps the weight change more gradual and realistic.
Either way, the number should come from a conversation with a doctor when there are underlying health conditions involved — reverse BMI is a planning convenience, not a clinical recommendation.
A worked example: from target BMI to a weight number
Quick answerFor a hypothetical person at 5'6" (66 in) who sets a target BMI of 23: weight = 23 × 66² ÷ 703 = 23 × 4,356 ÷ 703 ≈ 142.5 lb. That's the reverse-BMI target weight for that height and BMI.
The table below shows a few more example targets at the same height, purely to illustrate how the same formula scales — these are illustrative figures for a hypothetical 5'6" adult, not a personal recommendation:
Reverse BMI examples at a fixed height (5'6" / 66 in, illustrative only)
| Target BMI | Category | Matching weight |
|---|
| 19.5 | Low-normal | ~121 lb |
| 23.0 | Mid-normal | ~142.5 lb |
| 24.9 | High-normal | ~154 lb |
| 27.0 | Overweight | ~167 lb |
Note: the same target BMI produces a different weight at every height — a 5'6" person and a 6'0" person aiming for BMI 23 land on two very different scale numbers.
Not yet built into the calculatorA dedicated "reverse BMI" quick field — enter a target BMI and get the matching weight instantly, without doing the arithmetic by hand — is a natural addition to a BMI tool and may be added to the calculator in a future update. Until then, the formula above takes under a minute with a calculator app.
Turning a target weight into a realistic timeline
Quick answerA commonly cited pace for gradual, sustainable weight change is around 1 to 2 lb per week, driven by a calorie surplus or deficit relative to TDEE. A 15 lb gap, for example, suggests a rough illustrative range of 8 to 15 weeks — not a guarantee.
Once a reverse-BMI target weight exists, the next question is how long it might reasonably take to get there. That's where TDEE (total daily energy expenditure) comes back in: eating consistently below TDEE by a few hundred calories a day is the general mechanism behind gradual weight loss, and above it for gradual gain. Pairing a reverse-BMI target with a TDEE estimate turns "get to 142.5 lb" into an actual weekly plan, rather than a number floating in isolation.
It's also worth remembering that a target weight from reverse BMI, like BMI itself, doesn't know anything about muscle versus fat. Someone building muscle while losing fat might see the scale move more slowly than a pure calorie-math estimate would suggest — which is a good reason to track a body fat percentage estimate alongside the weight number, not instead of it.
Frequently asked questions
How do I find the weight that matches a target BMI?
Rearrange the standard BMI formula so weight is the unknown: weight (lb) = target BMI × height (in)² ÷ 703. For example, at 5'6" (66 inches) with a target BMI of 23: 23 × 66² ÷ 703 = 23 × 4,356 ÷ 703 ≈ 142.5 lb. This is sometimes called "reverse BMI" — starting from a BMI value and solving for weight instead of the other way around.
What target BMI should I actually pick?
There is no single universally "best" number — most people pick somewhere inside the CDC/WHO normal range of 18.5–24.9, often nearer the middle (around 21–23) rather than either edge, since both boundaries are transition points rather than optimal targets. The right choice depends on individual factors like frame size, muscle mass, and health history, which is why this is a starting point for a conversation with a doctor, not a fixed rule.
Is it better to set a weight goal or a BMI goal?
They describe the same thing in different units, so neither is inherently "better" — but a weight goal in pounds is often easier to track day to day on a home scale, while a BMI goal makes it easy to compare progress against the standard CDC/WHO categories. Converting a BMI target into a weight target (reverse BMI) lets you use whichever number is more motivating without losing the category context.
How much should a target weight change realistically over time?
A commonly cited pace for gradual weight change is roughly 1 to 2 lb per week, achieved through a calorie surplus or deficit relative to TDEE (total daily energy expenditure). For a hypothetical 15 lb gap between current weight and a target weight, that suggests a rough illustrative timeline of about 8 to 15 weeks — not a guarantee, since individual results vary and should be discussed with a healthcare provider.
Does a reverse BMI target account for body composition?
No. Like forward BMI, a reverse-calculated target weight is based only on height and a chosen BMI value, so it does not distinguish muscle from fat. Two people at the same target weight and height can have very different body compositions, which is why pairing a BMI-based target with a body fat percentage estimate gives a fuller picture than a weight number alone.