Geriatric Dose Calculator: Age and Renal Adjustments

Use the Geriatric Dose Calculator

Educational elderly dose adjustment guidance using Cockcroft–Gault dosing and renal dosing for older adults—age, CrCl, frailty, and hepatic context.

Enter inputs and calculate

How to Use Geriatric Dose Calculator: Age and Renal Adjustments

1. Step 1: Enter basics

   Add age, sex, weight, height, and serum creatinine. Use the kg/lb and cm/in toggles as needed.

2. Step 2: Pick medication sensitivity

   Select how renal‑sensitive the medicine is (Not, Mild, Moderate, High). If unsure, choose Moderate.

3. Step 3: Set clinical factors

   Choose frailty and hepatic impairment, and mark “narrow therapeutic index” if the drug requires extra caution.

4. Step 4: Calculate dose

   Tap Calculate to estimate creatinine clearance, a starting dose percentage, and interval guidance.

5. Step 5: Review & adjust

   Use the suggestion as an educational starting point only. Titrate to effect and follow prescriber labeling.

Key Features

• Age-aware dose suggestions
• Creatinine clearance (Cockcroft–Gault)
• Frailty and hepatic factors
• Narrow therapeutic index caution
• Interval adjustment guidance

Understanding Results

Formula

This calculator estimates kidney function using the Cockcroft–Gault equation, a common approach for drug dosing in adults: creatinine clearance (CrCl) ≈ ((140 − age) × weight) ÷ (72 × serum creatinine), multiplied by 0.85 for females. Weight selection follows widely used conventions: underweight patients use actual body weight; those near ideal use IBW; and in obesity an adjusted body weight may be used. Height is used to derive IBW (Devine formula) and, when indicated, adjusted body weight.

Reference Ranges & Interpretation

CrCl ≥ 60 mL/min is often considered normal/near‑normal for dosing; 30–59 suggests mild‑to‑moderate impairment; 15–29 indicates severe impairment; and < 15 reflects kidney failure. For many renally cleared medications, lower CrCl calls for a reduced starting dose and/or longer dosing intervals. Our geriatric dose calculator combines CrCl with age, frailty, hepatic status, and whether the drug is renal‑sensitive to produce a conservative starting percentage of the usual adult dose, along with interval guidance. Always prioritize the drug’s official labeling and prescriber instructions.

Assumptions & Limitations

Cockcroft–Gault is an estimate that can be biased in extreme body sizes, unstable renal function, or very low serum creatinine. The frailty and hepatic inputs are qualitative and meant to encourage cautious titration—not to replace clinical judgment. This tool does not diagnose, treat, or provide medical advice. Use it for education only and confirm all doses with authoritative sources. For general background on kidney function estimates, see the National Institute of Diabetes and Digestive and Kidney Diseases guidance on GFR estimation (opens in a new tab). NIDDK resource.

Complete Guide: Geriatric Dose Calculator: Age and Renal Adjustments

Use our geriatric dose calculator to estimate safe starting doses using age and creatinine clearance, with frailty and hepatic factors. Educational only.

What is this geriatric dose calculator?

The geriatric dose calculator is a mobile‑friendly educational tool that helps estimate a conservative starting point for dosing older adults. It blends age, estimated kidney function (via Cockcroft–Gault creatinine clearance), frailty, hepatic status, and a medication’s renal sensitivity to suggest a percent of the standard adult dose and to provide simple interval guidance. The goal is to support practical learning and safer decision‑making conversations—not to replace prescriber labeling or clinical judgment. We intentionally focus on transparent inputs and plain‑language outputs to support quick bedside or desktop workflows.

When should you use it—and for whom?

Use this calculator when you need a first‑pass sense of how age and kidney function may influence a medicine’s starting dose in older adults. It’s most helpful when a drug is renally cleared, when the patient appears frail, or when hepatic impairment is suspected. It is not specific to any one drug and does not replace professional guidance. If you need mg or mL conversions after you choose a percent, open our dose calculator (mg/mL) for concentration‑based math.

What inputs are required?

You’ll enter age, sex, weight, height, and serum creatinine. The tool automatically converts between kg/lb, cm/in, and mg/dL/µmol/L. Height is used to compute an ideal body weight (IBW), and when appropriate, an adjusted body weight (AdjBW). For renal function, we apply the Cockcroft–Gault equation using the weight most suitable for that body size profile. Then, you’ll choose whether the medication is Not, Mildly, Moderately, or Highly sensitive to renal impairment. Finally, you can mark frailty, hepatic impairment, and whether the drug has a narrow therapeutic index.

How this tool estimates renal function

Many dosing recommendations still reference Cockcroft–Gault creatinine clearance (CrCl) rather than eGFR because CG was used in original pharmacokinetic studies and labeling. Our calculator follows that convention. For background on kidney function estimates, you can also review eGFR using oureGFR calculator or evaluate renal clearance directly with ourcreatinine clearance calculator. In the dosing context, CG uses age, weight, sex, and serum creatinine to produce a mL/min value. We constrain the display to a practical range and categorize results as normal/near‑normal (≥ 60), mild–moderate (30–59), severe (15–29), or kidney failure (< 15) to support quick interpretation.

Weight selection in Cockcroft–Gault (IBW vs AdjBW vs actual)

Weight choice in CG is important. Using actual body weight in obesity may overestimate CrCl, while using IBW in underweight may underestimate it. Our logic is simple and transparent: if actual weight is below IBW, we use actual; if actual is within ~20% of IBW, we use IBW; if actual exceeds ~120% of IBW, we use adjusted body weight (IBW + 0.4 × (actual − IBW)). You can generate IBW on its own with ourideal body weight calculator. If you want surface‑ area‑based assessments for other clinical tasks, try our BSA calculator.

How the starting dose suggestion is calculated

The displayed percent is a conservative product of several factors: age, renal sensitivity, frailty, hepatic impairment, and whether the drug has a narrow therapeutic index. For example, an 82‑year‑old with moderate frailty and a highly renal‑sensitive medicine may see a substantial reduction, especially when CrCl is below 60 mL/min. Conversely, a robust 68‑year‑old on a medicine with minimal renal elimination may see little or no reduction. Because labeling varies by drug, the result is meant as a teaching aid and a reasonable first step before checking authoritative sources.

Interval guidance and what it means

For many renally cleared drugs, either the dose per administration is reduced, the dosing interval is extended, or both. The interval guidance displayed here maps to the CrCl category and the selected renal sensitivity level. As impairment deepens, interval extension becomes more likely. After you choose a percent, you can translate that into a real‑world dose using the strength on hand with ourdose calculator (mg/mL) and then consider the timing using the interval cue. If a drug’s half‑life matters for accumulation, thedrug half‑life calculator can help you visualize washout.

Frailty, hepatic impairment, and narrow therapeutic index

Frailty is a clinical pattern—reduced physiologic reserve, slower recovery, higher sensitivity to adverse effects. We add a modest downward adjustment for mild, moderate, and severe frailty to nudge starting doses lower. Hepatic impairment can also reduce drug clearance, especially for medicines with high first‑pass metabolism, so we include an additional reduction based on impairment severity. If your medicine has a narrow therapeutic index (e.g., small difference between effective and toxic concentrations), toggle the NTI option to apply an extra layer of caution and plan for closer monitoring. When hepatic function is central to a decision, consider using our Child‑Pugh calculator for structured staging and combine those insights with the dose suggestion here.

Worked examples

Example 1: A 78‑year‑old female, 64 in (163 cm), 63 kg, serum creatinine 1.0 mg/dL, mild frailty, no hepatic impairment, medicine with Moderate renal sensitivity. Cockcroft–Gault CrCl ≈ ((140−78)×IBW)/72×0.85. IBW is ~54.9 kg, so IBW is used. CrCl falls in the mild–moderate impairment range. Age, frailty, and sensitivity together might suggest starting near 65–75% of the usual adult dose with slightly extended intervals. Titrate to response and monitor.

Example 2: An 84‑year‑old male, 70 in (178 cm), 105 kg, serum creatinine 1.6 mg/dL, moderate frailty, mild hepatic impairment, medicine with High renal sensitivity and a narrow therapeutic index. IBW is ~73.6 kg; actual is > 120% of IBW, so adjusted body weight is used for CG. CrCl is in the severe range. The combined factors (age, severe renal impairment, frailty, hepatic impairment, NTI) may place the initial suggestion around 30–45% of the standard adult dose with a substantially extended interval. This is a starting point only—consult labeling and consider specialist input.

Example 3: A 69‑year‑old male, 68 in (173 cm), 68 kg, serum creatinine 0.9 mg/dL, no frailty, no hepatic impairment, medication Not renal‑sensitive. CG yields a CrCl in the normal/near‑normal range, and the tool may suggest ~95–100% of a usual adult dose with no interval change. You could still choose a more conservative start if other risks exist.

Limitations, safety, and practical next steps

No calculator can capture every nuance: rapidly changing renal function, atypical body composition, interacting drugs, and organ reserve can all affect dosing. Use this tool as a guide for discussion and a check on intuition. Next, review the medicine’s official labeling, see whether dosing tables are keyed to CrCl or eGFR, and verify the route and frequency adjustments. If you decide to adopt the suggested percent, convert it to an exact dose with thedosage calculator or themg/mL calculator, and if kidney status itself is the question, explore our kidney function calculator for a broader overview.

Finally, after a stable regimen is chosen, document the reasoning, monitor for efficacy and adverse effects, and revisit the dose with any change in renal function, clinical status, or concomitant therapies.

Common adjustment factors at a glance

In older adults, dose suggestions often reflect a blend of renal clearance, hepatic metabolism, body composition, frailty, and therapeutic index. Cockcroft–Gault (with an appropriate weight choice) remains widely used for drug labels keyed to creatinine clearance, while some guidance references eGFR. Consider which measure a label expects, then temper that with clinical context: hydration status, recent trends, dizziness/falls, and polypharmacy. The geriatric dose calculator surfaces these levers plainly so you can start conservatively and adjust based on response.

Documentation and follow‑up you can act on

Write down the inputs you used (weight basis for CG, renal category, frailty/hepatic selections) and the starting dose/interval you chose. Pair that with a simple monitoring plan: what you expect to improve, what adverse effects to watch, and when to re‑check renal labs. In practice, small changes go a long way—extend the interval first for renally cleared drugs, then adjust the dose if needed. Revisit assumptions after any acute illness, dehydration, or new medicine that can swing creatinine or hepatic workload.

Frequently Asked Questions