Map your ranch and see how many cattle it can carry.

Needs use the equations of the official NRC Nutrient Requirements of Beef Cattle model (8th ed., 2016; BCNRM software v1.0.37): maintenance (raised 20% while nursing for most breeds, adjusted for breed, body condition and terrain), milk (peak at 8.5 weeks; cows nursing their first calf, at 2 years old, give 88% of a mature cow's milk, with first-calf cows taken from your replacement rate), pregnancy (breed calf birth weight; energy for the calf converted at the diet's own efficiency) and intake (higher in late pregnancy). Needs are stated as lb of TDN at the month's forage quality: a lb of TDN in dormant grass carries less usable energy than a lb in a better diet, so a nursing cow on 48% TDN forage needs about a fifth more TDN than at the 63% diet where her intake would just cover her (the extension-table way). Milk levels scale your breed's own peak (Angus 17.6 lb, Simmental 26.5 lb at moderate). Checked against the BCNRM spreadsheet on 12 cow scenarios (nursing, pregnant, cold, wind, mud, heat): identical results.

Short grass: when the forage standing on the pastures (what cattle can still graze plus the stubble left standing) drops below about 1,030 lb/acre and there is little of it per head, cattle cannot bite off a full day's intake, so hay makes up the rest (NRC 2016 grazing intake factor, as coded in the BCNRM software). On a ranch stocked to its capacity this only happens in a deep drought.

Weather (when on) follows the same model: cows adapt to the previous month's temperature (needing more after cold months, less after hot ones); below the lower critical temperature — which depends on wind, hair depth (winter vs. summer coat), hide, a wet or muddy coat and body condition — they burn extra energy to stay warm. Calves get the same check, with the thin body insulation of a young calf (a calf under a month old feels cold much sooner than its mother); milk usually covers that extra energy. Panting in hot months adds 7–18%. Temperatures are the monthly normals for your region, so a single blue norther or ice storm is harder than the average shown.

Calves grow at the rate that reaches your average weaning weight. Their mother's milk is counted first; only the rest comes from pasture. When you wean on a date, calves born earlier are older and heavier. During the weaning period they eat like growing calves and are sold at the end of it.

Pasture is each pasture's forage (soil survey × range condition, or your estimate; ponds, brush and bottomland adjusted) times your harvest efficiency, spread over the year with NRCS ecological-site growth curves: for native range, the curve of the plant community that matches the range condition (Rolling Plains and Edwards Plateau); for improved pasture, hay meadows and small grains, the NRCS pasture and small-grain curves. Harvest efficiency is the grazing-system value on native range and at least 40% on improved pasture and 50% on small grains (Holechek); hay meadows are baled, not grazed, and their hay is fed before any is bought. Forage not eaten carries into the next month, losing 5% a month to weathering while the grass is dormant (Vallentine 2001). Steep ground counts less (Holechek: 11–30% slope −30%, 31–60% −60%, over 60% none), water only counts inside a pasture or on its fence, and rock outcrop and other non-producing soils count as zero. Quality uses typical diet values by month, not a forage test, or, if you choose it, what grazing cattle in your region select (B-6124, fecal samples). Young cows are lighter and still growing (BCNRM targets: 80% of mature weight at first calving, 92% at second, 96% at third), and first-calf cows give 88% of mature milk; their share of the herd comes from the replacement rate.

Intake follows Mississippi State Extension's guide (1.8–2.7% of body weight depending on forage quality). Herd intake uses the herd's average weight (young cows are lighter). When pasture runs out, hay fills the rest of the intake (bought or baled with your storage and feeding loss added, 15% by default); the supplement covers whatever protein or energy is still missing, and an energy supplement with more than 7 parts TDN per part protein replaces some grass (0.5 lb per lb). A month is flagged when degradable protein may fall under about 10% of the TDN eaten.

Losses: calf death loss is split into weather-related (about 10% of all losses in USDA's NAHMS study, adjusted by how cold the nights are in the birth month for your region) and everything else. Screwworm risk rises with temperature (little fly activity below 59°F, most at 77–86°F); there is no published loss rate yet, so you set it. Horn flies cut calf weaning weights 4–15% (UNL); the tool applies it to the share of nursing days in June–September.

Money: calves are sold at your market price slide (half steers, half heifers), cull cows at the cull-cow price, both from the site's shared market prices. By default it uses those prices as they are, like the other tools on this site. Turn on Seasonal prices to move them to the month you actually sell with a seasonal price pattern (calves: Oklahoma City 500–650 lb steers and 450–500 lb heifers, USDA 2016–2025, Feb–Apr about 3–4% above the year's average, October about 6% below; cull cows: San Angelo pattern, 1989–98). The result is cattle sales minus the feed you buy and the cost of feeding it — not profit: land, labor, vet, bull and other costs aren't in it.

Replacement heifers follow the BCNRM 2016 targets: 60% of mature weight when they settle at 15 months (65% for Brahman), 80% at first calving at 2 years, with growth and pregnancy needs from the same model. Enough heifer calves are kept to replace culls and dead cows after open heifers are sold at pregnancy check; culls are sold at weaning.

Body condition: if cows come off the calf thinner than your target, the energy to put it back (NRC 2016: a 1,100-lb cow needs about 207 Mcal to go from 4 to 5) is spread from weaning to a month before the next calving — the cheapest time to do it.

Not included: cold stress on calves, first-calf heifers, heifers you buy instead of raise. Growth curves, forage quality and weather are Texas data; outside Texas the tool uses the closest Texas region.