Clinical calculator · August 2026

Vancomycin calculator: vanco AUC and trough calculator from two timed levels

Enter the regimen and two timed steady-state levels. The calculator returns the elimination rate constant, half-life, extrapolated peak and trough, volume of distribution, clearance and the daily AUC, and it shows every step.

It reports pharmacokinetic quantities. It does not suggest a dose, an interval or a regimen change.

AUC or trough?

Runs entirely in your browser. Nothing you type is transmitted or stored.

Two timed levels, first-order

Estimate vancomycin AUC

Dose (mg) Interval (h) Infusion time (h)

Level 1, postdistributional peak

Concentration (mg/L) Hours after infusion end

Level 2, later in the same interval

Concentration (mg/L) Hours after infusion end

Estimate only. No dose is recommended. Verify before prescribing.

The short answer

How do you calculate vancomycin AUC?

Draw two timed steady-state levels in the same dosing interval, a peak 1 to 2 hours after the infusion ends and a trough later in the interval. Calculate the elimination rate constant from the two concentrations and the hours between them, extrapolate the true peak and trough, then add a linear trapezoid across the infusion to a log-linear trapezoid across the elimination phase. Scale that interval area to 24 hours. The 2020 ASHP, IDSA, PIDS and SIDP consensus guideline grades this two-level first-order method A-II and suggests a daily AUC of 400 to 600 mg·h/L for invasive MRSA infection.

Every guideline statement cited on this page was checked at its source in August 2026. Last updated August 2026.

What it needs

What the two-level method actually requires

Four things, and the one clinicians get wrong most often is the draw time rather than the concentration.

Dose

The dose that produced the two levels you are entering, not the dose you are considering next. The calculation describes the regimen the patient is already on.

Infusion time

hours

How long the bag actually ran. This matters more than clinicians expect, because the peak is extrapolated back to the end of the infusion.

Dosing interval

hours

The scheduled interval, usually 8, 12 or 24 hours. It sets how many intervals fit in a day and therefore scales the daily AUC.

Two timed levels

mg/L

A postdistributional peak drawn 1 to 2 hours after the infusion ends, and a trough later in the same interval, each with the exact time it was drawn.

Vancomycin is cleared almost entirely by the kidneys, so the renal picture sits upstream of every number this page produces. If you are working the problem from the other direction, starting from renal function rather than from measured levels, the creatinine clearance calculator handles the Cockcroft-Gault side, including the body weight choice that moves the answer more than most clinicians expect.

One practical warning about steady state. The first-order method assumes it, and in a patient whose renal function is still moving, it may simply not exist yet. Sepsis with augmented renal clearance, a patient coming off pressors, early acute kidney injury: in all three the half-life you calculate today describes a patient who will not be the same patient tomorrow. That instability is the strongest argument for Bayesian software, and it is the honest reason a department might buy one.

The arithmetic

The vancomycin AUC equations, step by step

Standard published first-order pharmacokinetics. Nothing here is proprietary and nothing is hidden.

Elimination rate constant

ke = ln(C1 / C2) / (t2 − t1)

The natural log of the ratio of the two concentrations, divided by the hours between them. Everything else on the page follows from this one number, which is why the draw times have to be recorded accurately rather than assumed from the order.

Half-life

t½ = 0.693 / ke

Useful as a sanity check before you trust the rest. A vancomycin half-life of 4 to 8 hours is ordinary in a patient with reasonable renal function. A wildly short or long value usually means a mistimed draw, not an unusual patient.

Extrapolated peak

Cmax = C1 × e^(ke × t1)

The measured peak is drawn after distribution is complete, so it sits below the true end-of-infusion concentration. Extrapolating back up the elimination curve recovers the value the trapezoid needs.

Extrapolated trough

Cmin = Cmax × e^(−ke × (tau − tinf))

Projects the concentration forward to the moment the next infusion starts. This is the true trough, which is often not the same as whatever the trough level happened to catch.

AUC over one interval

AUCtau = ((Cmax + Cmin) / 2) × tinf + (Cmax − Cmin) / ke

A linear trapezoid across the infusion, plus a log-linear trapezoid across the elimination phase. The two pieces together are the area under one complete dosing interval.

Daily AUC

AUC24 = AUCtau × (24 / tau)

Scaled to 24 hours, because the guideline target is expressed as a daily area. A patient on 1 g every 12 hours has two intervals in a day, so the interval area doubles.

Volume of distribution

Vd = (Dose / tinf) × (1 − e^(−ke × tinf)) / (ke × (Cmax − Cmin × e^(−ke × tinf)))

The Sawchuk-Zaske volume equation for an intermittent infusion. In adults a result near 0.5 to 0.9 L/kg is typical, and a figure far outside that range is worth investigating before acting on the AUC.

Clearance

CL = ke × Vd

Provides an independent check: total daily dose divided by clearance should land close to the trapezoidal AUC24. If the two disagree badly, one of the inputs is wrong.

A worked example, so the numbers are checkable. A patient on 1 g every 12 hours over a one hour infusion has a peak of 30 mg/L drawn one hour after the infusion ends and a trough of 10 mg/L drawn eleven hours after it ends. The rate constant is the natural log of 3 divided by 10 hours, or 0.110 per hour, giving a half-life of 6.3 hours. Extrapolating back gives a true peak of 33.5 mg/L and a true trough of 10.0 mg/L. The interval area is 235 mg·h/L, so the daily AUC is 471 mg·h/L. Clearance works out at 4.2 L per hour, and 2 g divided by 4.2 is 472, which is the cross-check landing where it should.

That cross-check is worth running every time. The trapezoidal route and the clearance route reach the daily AUC by different paths, so when they disagree by more than a few percent the usual cause is a draw time that was charted rather than observed.

The 2026 question

Is vancomycin AUC better than trough monitoring?

The 2020 consensus withdrew the trough-only target, and health systems are still working through what that costs.

Attribute	AUC-guided monitoring	Trough-only monitoring
What it measures	Total drug exposure across 24 hours, in mg*h/L	A single concentration at one moment in the interval
Guideline status, 2020 consensus	Recommended. AUC-guided dosing and monitoring is described as the most accurate and safest way to dose vancomycin	Trough-only monitoring with a 15 to 20 mg/L target is explicitly no longer recommended for serious MRSA infection
Target	400 to 600 mg*h/L daily, assuming a broth microdilution MIC of 1 mg/L	The old 15 to 20 mg/L band, which the guideline withdrew
Levels required	Two timed steady-state levels for the first-order method, or one to two with Bayesian software	One
Main argument for it	Exposure, not a single point, is what tracks efficacy and acute kidney injury risk	Cheaper, faster, and every nurse and lab already knows the workflow
Main argument against it	More draws, more arithmetic, and a real training burden across a nursing and pharmacy workforce	A trough in range is compatible with a daily exposure well above or well below the target

What is the vancomycin AUC goal?

The consensus guideline suggests maintaining daily AUC between 400 and 600 mg·h/L, assuming a broth microdilution MIC of 1 mg/L, to maximize efficacy and minimize the likelihood of acute kidney injury. The two bounds do different jobs. The floor is about treating the infection and the ceiling is about not damaging the kidney, which is why an AUC well above 600 is a finding rather than a comfort.

What is the difference between a vancomycin trough and a random level?

A trough is drawn at a defined point, immediately before the next dose, so it can be read against a reference range. A random level is drawn at an undocumented point in the interval and means very little on its own. The useful nuance is that a random level becomes fully usable the moment its exact draw time is recorded, because it can then serve as one of the two timed concentrations in an AUC calculation.

Can you calculate vancomycin AUC in Excel?

Yes. The first-order equations are ordinary arithmetic and fit comfortably in a spreadsheet, which is why so many departments run on one. The risk is version drift. Uncontrolled spreadsheets get emailed between clinicians, quietly edited, and stop matching the protocol they were built for, and nobody notices until an audit. If your department depends on one, give it an owner and a review date and treat it as a validated document.

Two graded methods

First-order equations or Bayesian software?

Both carry an A-II grade in the same guideline. They answer slightly different questions.

Two timed levels, first-order equations

Steady state reached, two draws obtainable

What the calculator on this page runs. The guideline states the AUC can be accurately estimated from two timed steady-state concentrations using first-order equations, and grades that A-II. It needs no software licence and it shows its working, which matters when a pharmacist has to defend the number at handoff.

Bayesian software with a population model

Early levels, non-steady state, or a single draw

Also graded A-II. Because it starts from a richly sampled population prior, it can work from one or two concentrations and does not require steady state, which is its real advantage on day one of therapy. It is a purchased product with a vendor behind it, and we do not sell one.

Trough-only estimation

Legacy protocols still in place

Still common in practice and still the default in some order sets. For serious MRSA infection the 2020 consensus withdrew the 15 to 20 mg/L trough target, so a protocol built on it is running against current guidance rather than alongside it.

Worth being direct about the commercial shape of this, because it affects how the advice reads elsewhere. Bayesian vancomycin dosing is a purchased product. We do not sell one, we have no reseller relationship with anyone who does, and there is nothing on this page we would gain from you buying or not buying. The two-level first-order method is free, it is graded A-II by the same guideline, and for a stable patient at steady state it does the job. Where Bayesian software genuinely earns its licence fee is the unstable patient and the single early level, and that is a real clinical argument rather than a marketing one.

ClinCalc, which is free on the web and maintained by an individual pharmacist author, implements both Bayesian modeling and the Sawchuk-Zaske method. It is a good tool. The thing a department has to weigh is that a free single-author site carries no vendor contract, no support path and no service commitment, which is a different risk profile from a licensed product even when the arithmetic is identical. We compared the wider field of drug dosing calculator apps for pharmacists separately.

Using the number

From a calculated AUC to a signed order

The calculator produces a measurement. A licensed prescriber produces the decision.

Confirm steady state first

First-order estimation from two levels assumes steady state, generally after roughly four to five half-lives on an unchanged regimen. Levels drawn before then describe a patient who is still accumulating, and the arithmetic will not know that.

Record the real draw times

Enter the times the samples were actually taken, not the times they were ordered. The elimination rate constant is driven entirely by the gap between the two draws, so a thirty minute charting error propagates through every result below it.

Read the outputs as measurements

AUC24, half-life, volume of distribution and clearance describe the regimen the patient is on right now. They are inputs to a decision about what to do next, not the decision itself.

Verify, then sign

Check the result against your institutional protocol and the official labeling, screen the regimen for interacting nephrotoxins, and let the licensed prescriber make and sign the dosing decision.

One thing the AUC number will never tell you is what else the patient is on. Vancomycin plus piperacillin-tazobactam is the best known example of a combination where the nephrotoxicity signal is stronger than either agent alone, and no pharmacokinetic calculation surfaces that, because it is an interaction question rather than an exposure question. Concurrent loop diuretics, contrast, ACE inhibitors and NSAIDs all sit in the same blind spot. That screen belongs beside the arithmetic, which is how the antibiotic dosing calculator and the drugs to avoid in renal failure reference are built to work.

Primary sources

Where every figure on this page comes from

Checked at the source, not repeated from a secondary summary.

2020 revised consensus guideline

Rybak MJ, Le J, Lodise TP and colleagues. "Therapeutic monitoring of vancomycin for serious methicillin-resistant Staphylococcus aureus infections: A revised consensus guideline and review by the American Society of Health-System Pharmacists, the Infectious Diseases Society of America, the Pediatric Infectious Diseases Society, and the Society of Infectious Diseases Pharmacists." American Journal of Health-System Pharmacy, 2020, volume 77, issue 11, pages 835 to 864. It states that daily AUC values, assuming a broth microdilution MIC of 1 mg/L, should be maintained between 400 and 600 mg*h/L to maximize efficacy and minimize the likelihood of acute kidney injury.

The two estimation methods, as graded

The same guideline grades both approaches A-II. It states the AUC can be accurately estimated from two timed steady-state concentrations using first-order equations, and separately supports Bayesian software embedded with a population model based on richly sampled data, working from one or two concentrations. It also records that trough-only monitoring targeting 15 to 20 mg/L is no longer recommended in serious MRSA infection.

Renal function as the upstream input

Vancomycin is renally cleared, so the kidney function estimate sits upstream of everything on this page. A 2025 National Kidney Foundation workgroup consensus in the American Journal of Health-System Pharmacy recommends moving away from Cockcroft-Gault estimated creatinine clearance toward the race-free 2021 CKD-EPI equation for medication decisions, individualized to body surface area.

Frequently asked

Vancomycin calculator questions

How do you calculate vancomycin AUC?

Draw two timed steady-state levels in the same dosing interval, a peak 1 to 2 hours after the infusion ends and a later trough. Calculate the elimination rate constant from the two concentrations and the hours between them, extrapolate the true peak and trough, then add a linear trapezoid across the infusion to a log-linear trapezoid across the elimination phase. Scale that interval area to 24 hours.

What is the vancomycin AUC goal?

The 2020 ASHP, IDSA, PIDS and SIDP consensus guideline suggests a daily AUC between 400 and 600 mg*h/L for invasive MRSA infection in adults and children, assuming a broth microdilution MIC of 1 mg/L. The lower bound reflects efficacy and the upper bound reflects acute kidney injury risk. Your institutional protocol governs how it is applied.

Is vancomycin AUC better than trough monitoring?

For serious MRSA infection the consensus guideline says yes, describing AUC-guided dosing and monitoring as the most accurate and safest approach, and it explicitly withdrew the old trough-only target of 15 to 20 mg/L. A trough sitting comfortably in range is entirely compatible with a daily exposure above or below the AUC target, which is the practical reason the recommendation changed.

How many levels do you need to calculate vancomycin AUC?

Two timed steady-state levels if you are using first-order equations, which is the method this calculator runs. Bayesian software can work from one or two concentrations and does not require steady state, though the guideline still notes it is preferable to obtain two samples, typically at 1 to 2 hours after the infusion and at the end of the interval.

How do you calculate vancomycin half life?

Divide 0.693 by the elimination rate constant. The rate constant is the natural log of the peak concentration divided by the trough concentration, divided by the hours between the two draws. A half-life of roughly 4 to 8 hours is ordinary in an adult with reasonable renal function, and a value far outside that usually points to a mistimed sample.

How do you calculate vancomycin clearance?

Multiply the elimination rate constant by the volume of distribution. Volume comes from the Sawchuk-Zaske equation for an intermittent infusion, using the dose, the infusion time and the extrapolated peak and trough. As a cross-check, total daily dose divided by clearance should land close to the trapezoidal daily AUC.

When should you check a vancomycin trough?

Conventionally at steady state, immediately before the next dose, which is generally after four to five half-lives on an unchanged regimen. For AUC estimation by first-order equations the trough is paired with a postdistributional peak drawn in the same interval, and both draw times have to be documented rather than inferred from the administration record.

What is the difference between a vancomycin trough and a random level?

A trough is drawn at a defined point, immediately before the next dose, so it can be compared against a reference range. A random level is drawn at an undocumented point in the interval, which makes it uninterpretable on its own. A random level does become usable if the exact draw time is recorded, because then it can serve as one of the two timed concentrations in an AUC calculation.

Can you calculate vancomycin AUC in Excel?

Yes, the first-order equations are ordinary arithmetic and fit in a spreadsheet. The risk is version drift: uncontrolled spreadsheets circulate between clinicians, get edited, and stop matching the protocol they were built for. If your department relies on one, treat it as a validated document with an owner and a review date rather than as a file someone emailed around.

Does this calculator recommend a vancomycin dose?

No. It reports pharmacokinetic quantities calculated from the levels you enter: rate constant, half-life, extrapolated peak and trough, volume of distribution, clearance and daily AUC. It does not suggest a dose, an interval or a regimen change. Those decisions belong to the licensed prescriber, working from institutional protocol and official labeling.

Keep going

Renal function, antibiotic dosing and what to license

Creatinine clearance calculator

Cockcroft-Gault with the weight basis you choose, plus whether the label wants CrCl or eGFR.

Antibiotic dosing calculator

Renal adjustment surfaced beside the interaction screen instead of as a separate lookup.

Drugs to avoid in renal failure

The nephrotoxins that sit in a pharmacokinetic calculation's blind spot.

Renal dosing calculator

Where the clearance estimate meets the labeled dosing band for the specific drug.

Drug dosing calculator apps compared

MDCalc, ClinCalc, Epocrates and Lexidrug, with every published price verified.

Best drug reference app

What each reference actually licenses, and what none of them publish.

Prescriber.io

The exposure is only half the check.

A vancomycin AUC tells you about the drug. It says nothing about the nephrotoxin sitting two lines below it on the same medication list. Prescriber.io surfaces interactions, contraindications and renal dosing in one pass, before you sign.