Fiber & Protein Calculator
How much do you need?
Source: Institute of Medicine, Dietary Reference Intakes (2005). Active protein range per Jäger et al., 2017, J. Int. Soc. Sports Nutr.
Why Your Fiber and Protein Gap Matters
Fiber and protein are two nutrients most people track the least — yet shortfalls in either are linked to real health outcomes. Low fiber intake is associated with higher rates of cardiovascular disease, type 2 diabetes, and colorectal issues. Most adults in the U.S. get only 15g of fiber per day, roughly half the recommended amount.
Protein is less commonly under-consumed, but it matters for maintaining muscle mass, supporting immune function, and recovering from physical activity. The RDA of 0.8g per kg of body weight is a minimum to prevent deficiency — not an optimal target for active people.
A gap between what you eat and what the research recommends is worth knowing about. This calculator gives you those numbers so you can make informed choices about your diet.
How These Numbers Are Calculated
The fiber targets come directly from the Institute of Medicine's Dietary Reference Intakes: 25g/day for adult women (19–50), 38g/day for adult men (19–50), adjusted down to approximately 21g and 30g respectively after age 50.
Protein is calculated at 0.8g per kilogram of body weight — the RDA minimum established by the Institute of Medicine. If you enter your weight, you'll also see an "active range" of 1.2–1.6g/kg, which is widely cited in sports nutrition research as beneficial for people who exercise regularly. These are two different standards: the RDA is a population-level minimum, while the active range is an evidence-based recommendation for physically active individuals.
If you provide your current daily intake, the calculator shows the gap between what you eat and these reference values. All figures are general population data — not personalized medical advice.
Based on NIH Dietary Reference Intake values. Last updated: July 2026. DRI values from the Institute of Medicine (2005). Active protein range per Jäger et al. (2017).
Frequently Asked Questions
How much fiber do I need per day?
The NIH recommends 25g of fiber per day for adult women and 38g for adult men. Adults over 51 need slightly less: 21g for women and 30g for men.
How much protein do I need per day?
The minimum RDA is 0.8g of protein per kilogram of body weight. Active individuals and those building muscle typically benefit from 1.2–1.6g per kg, though this is above the minimum RDA.
What happens if I don't get enough fiber?
Low fiber intake is linked to higher rates of cardiovascular disease, type 2 diabetes, and colorectal issues. Most adults in the US consume around 15g per day — roughly half the recommended amount.
Is this calculator based on official guidelines?
Yes. Fiber targets use the NIH Dietary Reference Intake values. Protein targets use the standard RDA of 0.8g/kg with an optional active range of 1.2–1.6g/kg from sports nutrition literature.