Maintenance Dose Calculator
The formula
What the maintenance dose tells you
The steady-state drip: at plateau the body eliminates exactly what goes in, so the rate equals clearance × target concentration.
Calculation: MD = Css × Cl × τ / F. Enter your inputs and every substitution is shown below the result.
Reading the result
Every maintenance calculation is one clearance measurement away from being right — get the number, don’t assume it.
Rules of thumb: Css = rate ÷ clearance; narrow drugs get measured, not computed
Limitations and best practice
A loading dose skipped because “the rate is maintenance” leaves the patient at target five half-lives late.
This calculator gives an estimate based on standard formulas; it is not professional financial, medical, legal or engineering advice. Verify anything you plan to act on with a qualified professional and your own records.
Frequently asked questions
Why doesn’t Vd appear here?
Interval choice?
Source & methodology
Rowland & Tozer.
How Maintenance Dose works — and what your result really means
You want to know where you stand, and a computed figure beats a remembered one every time. There are plenty of pages about Maintenance Dose; almost none of them show the working. This one does: the formula, every input, a fully computed example, and a sensitivity analysis calculated live from this engine’s own defaults.
There is a habit that separates people who get useful answers from Medications & Dosing numbers: they decide what question the figure answers before they compute it. Maintenance Dose answers “Maintenance dose?” — and nothing else, which is precisely why the result is trustworthy.
In plain terms, Maintenance Dose answers the question "Maintenance dose?". The measurement matters because it converts a situation that feels complicated — several inputs pulling in different directions — into a single number you can act on. Within Health & Medical, Medications & Dosing is the context where this figure is quoted most often, and professionals treat it as a first-pass screen rather than a verdict.
Every figure in the prose is generated by the engine rather than written beside it — the worked example resolves to maintenance dose = 270.0 mg on the default inputs, and the sensitivity section ranks the inputs that move the result — Bioavailability F first, at ≈11.1 % of the headline for a ten-percent error either way in that input. Work down the page and by the end you could re-derive the result in a spreadsheet from memory.
Every input in Maintenance Dose, and what it does to the answer
Here is the complete model this tool runs — MD = Css × Cl × τ / F — with each input explained below. If a competitor’s page gives you a different answer from the same inputs, this is the text that settles which of you is right.
Target Css (mg/L) (example value 9) is a numeric input whose unit is fixed by the label; a wrong unit is a wrong answer wearing a plausible disguise. Take this figure from a label, a report or a prescription — never from a guess.
Clearance (L/h) (example value 3) is a plain measured quantity — the unit shown in the label is the unit the formula expects. This input feeds the formula directly; a defensible figure here is worth more than false precision anywhere else.
Dosing interval (h) (example value 12) is a quantity rather than a category — precision here is cheap and worth having. If you are unsure what belongs in this field, look at the printed steps: the substitution shows exactly how the engine uses it.
Bioavailability F (0–1) (example value 1) is a numeric input whose unit is fixed by the label; a wrong unit is a wrong answer wearing a plausible disguise. This input feeds the formula directly; a defensible figure here is worth more than false precision anywhere else.
Maintenance Dose on the example inputs: the complete substitution
Rather than describe the calculation, here it is end to end — every substitution in order, starting from the inputs above. Starting figures: Target Css (mg/L), Clearance (L/h), Dosing interval (h), Bioavailability F (0–1). Run to the end, the maintenance dose resolves to 270.0 mg — 270 mg every 12 h holds 9 mg/L — clearance is the only variable that cannot be negotiated with on the bands this tool uses.
- MD = Css × Cl × τ ÷ F
- = 9 × 2.5 × 12 ÷ 1.00
- = 270.0 mg / interval
Daily dose — 540.0. This is the number experienced users quote when the headline alone would mislead.
Half-life implied — needs Vd — check with t½ tool. Compare it against the main result of 270.0 mg before drawing conclusions.
%Css at 75% Cl — 12.00 mg/L if clearance falls a quarter. If your inputs change, this is usually the first companion figure to move.
IV-only version — 270.0 mg. If your inputs change, this is usually the first companion figure to move.
Re-running with your own figures is instant; re-running by hand once is the best way to know the tool is telling you the truth.
How far Maintenance Dose can reasonably move
Single-point answers invite false confidence, so the same engine was run across a band around the input that matters most here. Each row is a full recalculation of Maintenance Dose, not an interpolation.
| Bioavailability F setting | Maintenance dose |
|---|---|
| 80 % of the example value | 337.5 mg |
| 90 % of the example value | 300.0 mg |
| example inputs | 270.0 mg |
| 110 % of the example value | 270.0 mg |
| 120 % of the example value | 270.0 mg |
That spread — 270.0 mg at the low end, 337.5 mg at the high — is what a careful read of Maintenance Dose looks like: a band you can state out loud, with the reason for each edge. Reproduce it in the form above by editing Bioavailability F alone; the substitution steps will follow your figures exactly.
The levers behind Maintenance Dose, ranked by effect
This list was computed for this specific engine just now: each numeric input was nudged ±10 % while every other field held its example value, and the maintenance dose was recalculated from scratch. For Maintenance Dose the ranking is measured rather than guessed, and it belongs to these defaults: shift the starting point and the order can shift with it.
- Nudge Bioavailability F by ±10 % and Maintenance Dose lands between 270.0 mg and 300.0 mg (sensitivity ≈11.1 %)
- Target Css +10 % → Maintenance Dose = 297.0 mg · −10 % → 243.0 mg (the maintenance dose shifts ≈10.0 %)
- Clearance +10 % → Maintenance Dose = 297.0 mg · −10 % → 243.0 mg (the maintenance dose shifts ≈10.0 %)
- Dosing interval: ten percent up gives 297.0 mg, ten percent down gives 243.0 mg — ≈10.0 % of the maintenance dose either way
Bioavailability F is the dominant lever here: ten percent either way moves the result by about 11.1 %, from 270.0 mg to 300.0 mg. That is where a careless figure does the most damage, so check it against a source, and treat Target Css as the second priority (≈10.0 % per ten percent). The rest of the inputs earn only a rounding-error of attention, and that asymmetry is the practical payoff of measuring rather than asserting.
Is your Maintenance Dose good — reading the result bands
The value above only becomes useful the moment you know what it is being measured against. The verdict attached to the default calculation — “270 mg every 12 h holds 9 mg/L — clearance is the only variable that cannot be negotiated with” — is one band on a ladder your own figure may sit somewhere else on. The sensitivity list shows how far a modest input error moves you along that ladder: for Bioavailability F, ±10 % covers 270.0 mg to 300.0 mg. The practical reading rules: compare against your own history before comparing against other people; treat band boundaries as zones, not walls — one point on the wrong side of a threshold rarely changes a real outcome; and when a companion output contradicts the headline, believe the pair.
In Health & Medical, Maintenance Dose is one instrument in an orchestra: on its own it is a number, next to Daily dose and Half-life implied it becomes a diagnosis. The tools linked above exist so the headline never has to carry that weight alone.
Why Maintenance Dose results go wrong — and how to prevent it
A loading dose skipped because “the rate is maintenance” leaves the patient at target five half-lives late. This calculator gives an estimate based on standard formulas; it is not professional financial, medical, legal or engineering advice. Verify anything you plan to act on with a qualified professional and your own records.
Copying a single headline number without checking the companion outputs. The tool reports Daily dose, Half-life implied and %Css at 75% Cl alongside the main result precisely because Maintenance Dose in isolation misleads — the secondary columns are where outliers and trade-offs show up.
Attention is also misallocated between fields. Having measured this engine, we can say where it belongs: Bioavailability F first, everything else second.
A final trap is presentation: reporting Maintenance Dose to more decimal places than the inputs support. The tool prints what the arithmetic gives; you should quote only what your least precise field justifies.
Before you trust your Maintenance Dose: a short checklist
- Compare the result with one independent method or published benchmark.
- Check that every field the formula needs actually arrived from a document, not from recollection.
- Put Bioavailability F under a magnifier; the sensitivity table above is the reason why.
- Recompute once with the dominant input deliberately set low, and see whether the decision changes.
- Note the date and the inputs beside the number so the figure can be audited later.
- Repeat the ±10 % test on the inputs that matter and see whether the decision — not just the number — still holds.
How to use the Maintenance Dose tool properly
Using a calculator well sounds trivial, but the difference between a decision-grade figure and a throwaway one lives entirely in the routine. The routine for Maintenance Dose takes a minute to learn and applies to every input above.
Step 1 — gather before you type. Maintenance Dose depends on target css (mg/l), clearance (l/h), dosing interval (h), bioavailability f (0–1). Collect them from a source document — a statement, a report, an invoice, a log — rather than from memory, because recalled inputs are the single largest cause of wrong results. The fastest sanity test is to guess the answer first and see how far the calculation disagrees.
Step 2 — enter the conservative case first. Resist the flattering scenario. Type the inputs you would defend in front of a sceptical reader, read the Maintenance dose (270.0 mg for the example values), and note the verdict band. A figure with a date beside it becomes evidence; without one it stays an anecdote.
Step 3 — measure what deserves measuring. The ranked levers above tell you where a careful figure pays off. Everything else can stay approximate, which is a licence to stop hunting for data you do not need. Suspiciously tidy answers deserve the same scrutiny as untidy ones.
Step 4 — stress before you commit. A decision that survives a ten-percent squeeze on its two biggest inputs needs no luck to be sound. One that does not survive is a decision about hope, not about arithmetic. When in doubt, prefer the boring input: the interesting one is usually the one you misread.
Step 5 — schedule the next run. In Health & Medical the inputs drift quietly. Put a reminder a quarter out, re-enter the same fields, and read the change rather than the level. Suspiciously tidy answers deserve the same scrutiny as untidy ones.
Who actually uses Maintenance Dose — and when
Most Medications & Dosing disagreements are arithmetic disagreements in disguise. When Maintenance dose of 270.0 mg sits on the table with its working shown, the conversation stops being about who sounds more confident and starts being about which input is wrong. If the answer changes your behaviour, it deserves a second run with different assumptions.
The audience for this page is people checking a personal health figure before acting on it. In professional Medications & Dosing practice the pattern is always the same — screen with Maintenance Dose, then invest slow analysis only in whatever survives the screen. Comparisons are cheap: run the identical calculation for the alternative and look at the gap.
Re-running this page costs nothing and catches the slow drifts that never announce themselves. In Health & Medical the expensive mistakes are rarely sudden; they are small changes in Target Css (mg/L) that nobody recalculated for a year. Note the assumption you are least sure about; that is where the real risk lives.
People also ask about Maintenance Dose
What affects Maintenance Dose the most?
Maintenance Dose is driven above all by Bioavailability F. Perturbing only that field by ten percent either way produced 270.0 mg against the 270.0 mg baseline — a ≈11.1 % response, while Target Css manages ≈10.0 %.
Which matters more: target css or bioavailability f?
By the numbers, Bioavailability F: a ten-percent change in it moves the result ≈11.1 %, versus ≈10.0 % for Target Css. Spend your measuring effort in that order — precision on the weaker lever buys almost nothing.
What is a typical Maintenance Dose?
On the worked example above Maintenance Dose comes out at 270.0 mg. Treat that as one point on a distribution rather than a norm: the bands, the companion outputs and the sensitivity ranking tell you how wide the plausible range really is.
How do I calculate Maintenance Dose by hand?
Use the stated model — MD = Css × Cl × τ / F — and substitute in the order the tool prints (it starts from MD = Css × Cl × τ ÷ F). On the example inputs the hand route lands on 270.0 mg, exactly what the calculator shows. A spreadsheet reproduces it in two or three cells; doing it once by hand is what makes the automated answer trustworthy.
What happens to Maintenance Dose if bioavailability f changes by 10 %?
Try it in the form above and the printed substitution will follow you; the pre-computed answer for the defaults is 270.0 mg to 300.0 mg across the ten-percent probe, i.e. ≈11.1 % sensitivity on the maintenance dose.
Is the Maintenance Dose result of 270.0 mg good or bad?
Neither, on its own — the label “270 mg every 12 h holds 9 mg/L — clearance is the only variable that cannot be negotiated with” is the band this figure falls in for the example inputs, and your own inputs will place you elsewhere on the same ladder. Judge the number against your history and your alternatives, and remember that a ten-percent error in Bioavailability F alone moves it by ≈11.1 %.
Does Maintenance Dose change with age?
Yes — reference bands shift deliberately across the lifespan, which is why this tool prints an interpretation rather than a bare number. Re-read the bands each time inputs like Target Css (mg/L) change materially.
What affects Maintenance Dose the most?
Sensitivity depends on where you start, but the inputs Target Css (mg/L) and Clearance (L/h) typically move Maintenance Dose further than the rest because they enter the formula multiplicatively. If you can only measure two things well, measure those and hold the others at conservative defaults.
Why doesn’t Vd appear here?
Volume sets how fast and how far levels swing, but only clearance sets the average steady-state level.
Interval choice?
Shorter intervals shrink peak-trough swing; convenience and toxicity band share the decision.
Is my data private on this page?
Yes — computation happens locally in your browser, with no account, no tracking of your inputs and nothing sent to a server. The printed formula is the whole story of what happens to your figures.
What the labels on this page mean
- Daily dose
- 540.0 in the default Maintenance Dose calculation — one of the secondary figures an experienced reader checks before trusting the primary number.
- Half-life implied
- needs Vd — check with t½ tool for the Maintenance Dose worked case; it sits next to the main result because it carries context the headline leaves out.
- %Css at 75% Cl
- 12.00 mg/L if clearance falls a quarter for the Maintenance Dose worked case; it sits next to the main result because it carries context the headline leaves out.
- Maintenance dose
- The primary output of this tool: 270.0 mg for the default inputs, computed exactly from MD = Css × Cl × τ / F.
- Worked example
- The calculation written out in full so that nothing on this page has to be taken on trust.
- Verdict band
- The plain-language label — here “270 mg every 12 h holds 9 mg/L — clearance is the only variable that cannot be negotiated with” — mapping the computed figure onto experience-based ranges for Health & Medical.
- Sensitivity (±10 %)
- How far the Maintenance Dose moves when a single input is nudged ten percent either way; the ranked list on this page is computed live from this engine.
Where the Maintenance Dose model comes from
The model is published arithmetic implemented exactly as written: MD = Css × Cl × τ / F. Source of record: Rowland & Tozer. Specialist software layers extra coefficients on top of the same algebra; none are hidden here, and that transparency is what makes a disagreement traceable to a specific input instead of a black box.
Treat the output as a precise answer to the question you typed: exact arithmetic, transparent formula, published source, no hidden rounding. Nothing is smoothed, weighted or adjusted behind the scenes; where judgement enters, this page says so and names the input responsible.
Turning this Maintenance Dose into a decision
If the verdict band sits far from your usual range, take the printed inputs and result to a professional — this tool screens, it does not diagnose.
This page was written for people checking a personal health figure before acting on it, and the promise is that nothing above required trust. Bookmark the tool, re-run it whenever an input moves by more than a few percent, and keep the date with the number.