Fiber Intake CalculatorHow Much Fiber Do I Need Per Day?
Get your daily fibre target by age, sex or calories. Estimate what you eat now with a quick food check, then close the gap with a gradual week-by-week ramp-up that avoids bloating.
Built & medically reviewed by Manzoor Ahmad, Pharmacist & Calculator Developer · Updated
Targets from the National Academies DRIs and Dietary Guidelines. Health outcomes from Reynolds et al., Lancet 2019.
How much fibre do you need a day?
Adult women need about 25 g of fibre a day (21 g after age 50) and men about 38 g (30 g after 50). That works out to 14 g per 1,000 calories. Most adults eat only about 15 g. Increase by around 5 g a week with extra water to avoid bloating.
Your fibre
Most adults get only about 15–16 g a day.
You’re getting about 14 g, so the gap is 11 g.
Close the gap with any one of these
Ramp up slowly (avoids bloating)
How much fibre do you need per day?
| Group | Adequate intake | Notes |
|---|---|---|
| Women 19–50 | 25 g | ≈ 14 g per 1,000 kcal |
| Women 51+ | 21 g | |
| Men 19–50 | 38 g | |
| Men 51+ | 30 g | |
| Pregnancy | 28 g | |
| Breastfeeding | 29 g | |
| Teens 14–18 | Boys 38 g · Girls 26 g |
How your target is set
Large reviews (Reynolds et al., Lancet 2019) found that 25–29 g a day is linked to 15–30% lower rates of heart disease, type 2 diabetes and bowel cancer, with further benefit above 30 g.
Woman, 30, typical day
- Target: 25 g
- Yesterday: 2 fruit (6 g), 2 servings of vegetables (5 g), 1 slice of wholegrain bread (2 g), 2 servings of white rice (1.4 g) ≈ 14 g
- Gap: 11 g. Half a cup of oats with chia and a pear closes it.
- Ramp-up: 14 → 19 → 24 → 25 g over 3 weeks.
Fibre supplements and your medicines
Bulk-forming fibre (psyllium/ispaghula, methylcellulose) can bind to or slow the absorption of medicines. Take levothyroxine, digoxin, lithium, carbamazepine, warfarin and iron at least 2 hours apart from fibre supplements. Always take psyllium with a full glass of water, because taken dry it can cause choking or blockage. Psyllium also lowers LDL cholesterol by about 5–10%, a genuine bonus alongside statins.
If you have IBS, soluble fibre (psyllium, oats) is usually better tolerated than insoluble bran. With Crohn’s strictures, follow your gastroenterologist’s low-residue advice.
Related calculators
Fiber Intake calculator FAQs
Women need about 25 g a day (21 g after 50) and men about 38 g (30 g after 50), according to the National Academies. Another way to calculate it is 14 g for every 1,000 calories you eat.
A sample day: oats with chia and berries (10 g), a lentil or bean salad (8 g), an apple and a pear (9 g), and two cups of vegetables (5 g) adds up to over 30 g. Increase gradually.
A sudden big increase often causes gas, bloating and cramps, and sometimes constipation if you don’t drink enough water. Add about 5 g a week and drink more fluids.
You need both. Soluble fibre (oats, beans, psyllium) lowers cholesterol and steadies blood sugar. Insoluble fibre (wholegrains, vegetable skins) keeps you regular. Eating a varied range of plant foods covers both.
Yes, they count toward your total, and psyllium has good evidence for cholesterol and bowel health. Whole foods add vitamins, polyphenols and a wider mix of fibre types, so use supplements to top up rather than replace food.
Bulk-forming fibre supplements can reduce or delay absorption of some medicines, including levothyroxine, digoxin, lithium, carbamazepine and iron. Take them at least 2 hours apart.
Manzoor Ahmad
Pharmacist · Supplement & Nutrition Writer (9+ yrs) · Calculator Developer (13+ yrs)
I’m a practising pharmacist and DexoCalc’s developer. People buy psyllium from me every day, often without knowing it can block absorption of their thyroid or heart medicine. So this calculator pairs a food-first fibre plan with clear supplement timing rules.
References
- Reynolds A, et al. Carbohydrate quality and human health. Lancet. 2019;393(10170):434–445. PubMed
- Institute of Medicine. Dietary Reference Intakes: Fiber.
- Jovanovski E, et al. Effect of psyllium fiber on LDL cholesterol. Am J Clin Nutr. 2018;108(5):922–932. PubMed
- USDA. FoodData Central (fibre values).
Medical disclaimer: General guidance for healthy adults, not medical advice. If you have bowel disease, strictures or swallowing difficulties, or take medicines affected by fibre, ask your doctor or pharmacist first.