Lithium Dose Calculator
The formula
What the lithium maintenance tells you
Renal-function-driven lithium dosing: the ion is handled almost entirely by the kidney, so dose equals target concentration times its clearance.
Calculation: Dose = target × Cl_Li; Cl_Li (L/day) ≈ 0.25·CrCl + 3; 37.5 mg per mmol. Enter your inputs and every substitution is shown below the result.
Reading the result
Prophylaxis levels 0.6–0.8 mmol/L cut relapse with less burden than 1.0; the dose is a level-prescribing exercise.
Rules of thumb: Typical maintenance 600–900 mg/day ER at normal renal function
Limitations and best practice
NSAIDs, ACE inhibitors and thiazides all shrink lithium clearance within days — any new antihypertensive demands a re-level.
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 12-hour levels?
Is weight used at all?
Source & methodology
NICE CG185 monitoring; Ritschel pharmacokinetics.
Lithium Dose explained: formula, worked example and honest limits
You want to know where you stand, and a computed figure beats a remembered one every time. Lithium Dose is the kind of number people argue about from memory. This page ends that argument with arithmetic you can watch happen: enter your figures, get Daily dose in real time, and see every substitution printed below.
In plain terms, Lithium Dose answers the question "Daily 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.
The useful way to hold Lithium Dose is as a ratio with a story attached: Dose = target × Cl_Li; Cl_Li (L/day) ≈ 0.25·CrCl + 3; 37.5 mg per mmol says how the parts combine, and the 750 mg/day figure above is simply that sentence written in numbers. Everything that follows unpacks one clause of the sentence at a time.
Nothing below is stock text pasted around a number: the worked example computes daily dose = 750 mg/day from this tool’s own defaults, and the sensitivity section ranks the inputs that move the result — CrCl first, at ≈20.0 % 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.
Inside the Lithium Dose calculation: formula and every input
Here is the complete model this tool runs — Dose = target × Cl_Li; Cl_Li (L/day) ≈ 0.25·CrCl + 3; 37.5 mg per mmol — 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.
CrCl (mL/min) (example value 95) is a plain measured quantity — the unit shown in the label is the unit the formula expects. Figures of this kind carry safety consequences; when in doubt, use the conservative value and confirm with a professional.
Target level (mmol/L) (example value 1) is a quantity rather than a category — precision here is cheap and worth having. This input feeds the formula directly; a defensible figure here is worth more than false precision anywhere else.
Weight (kg) (example value 110) is a quantity rather than a category — precision here is cheap and worth having. Stay in one unit system top to bottom; conversion rounding is where small errors enter.
Formulation (example value Immediate (ER given as divided)) is a choice rather than a quantity — pick the option that matches your situation, because the calculation path branches here. The example value is there to demonstrate the mechanics, not to describe your situation — overwrite it.
What each “Formulation” choice actually does: Immediate (ER given as divided) → 750 mg/day · ER/controlled-release → 900 mg/day — each value above is the model’s own output for that option, so the choice can be made on evidence rather than on what a category feels like it means.
Lithium Dose on the example inputs: the complete substitution
Abstract formulas are hard to trust, so here is the complete substitution using the default inputs, written the way an examiner would want it. Starting figures: CrCl (mL/min), Target level (mmol/L), Weight (kg), Formulation. The computed daily dose comes out at 750 mg/day, which the interpretation band labels “A target of 0.8 mmol/L with CrCl 95 implies lithium clearance of 26.8 L/day → 21.4 mmol/day ≈ 750 mg — level check 5 days apart until two steady readings, narrow therapeutic index applies”.
- Cl = 0.25 × 95 + 3 = 26.8 L/day
- mmol = 0.8 × 26.8 = 21.40
- × 37.5 mg/mmol → 803 mg/day
Computed mg/day — 803. This is the number experienced users quote when the headline alone would mislead.
Per dose (BD) — 401 mg. Read next to the headline, this is the figure that shows the shape of the trade-off.
mmol/day — 21.40. If your inputs change, this is usually the first companion figure to move.
10-day check — level 12-h post dose (ER). Read next to the headline, this is the figure that shows the shape of the trade-off.
Overwrite any input above and every line of this example updates with it — the substitution is live, not a screenshot of somebody else’s numbers.
How far Lithium Dose can reasonably move
Read this table as the practical error bar on the headline figure. It answers the question people actually have after seeing a single number: how wrong could this be if the main input is off by ten or twenty percent?
| CrCl setting | Daily dose |
|---|---|
| 80 % of the example value | 600 mg/day |
| 90 % of the example value | 750 mg/day |
| example inputs | 750 mg/day |
| 110 % of the example value | 900 mg/day |
| 120 % of the example value | 900 mg/day |
That spread — 600 mg/day at the low end, 900 mg/day at the high — is what a careful read of Lithium Dose looks like: a band you can state out loud, with the reason for each edge. Reproduce it in the form above by editing CrCl alone; the substitution steps will follow your figures exactly.
What actually moves your Lithium Dose
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 daily dose was recalculated from scratch. Read it as a map of where Lithium Dose is fragile — drawn for the example inputs, which is the map you want when deciding what to measure carefully.
- CrCl +10 % → Lithium Dose = 900 mg/day · −10 % → 750 mg/day (the daily dose shifts ≈20.0 %)
- Target level: ten percent up gives 900 mg/day, ten percent down gives 750 mg/day — ≈20.0 % of the daily dose either way
CrCl is the dominant lever here: ten percent either way moves the result by about 20.0 %, from 750 mg/day to 900 mg/day. Measure that input from a document rather than from memory, and Target level is effectively tied with it (≈20.0 % for the same nudge), so verify the pair together. Everything below that can stay approximate, which is a licence to stop chasing data that would not change the decision.
Is your Lithium Dose good — reading the result bands
A number on its own is trivia; a number against a range is intelligence. On the example inputs the band reads “A target of 0.8 mmol/L with CrCl 95 implies lithium clearance of 26.8 L/day → 21.4 mmol/day ≈ 750 mg — level check 5 days apart until two steady readings, narrow therapeutic index applies”; your own figures place you on a different rung of the same ladder. The sensitivity list shows how far a modest input error moves you along that ladder: for CrCl, ±10 % covers 750 mg/day to 900 mg/day. The practical reading rules: ask what would have to change to move you one band. If the answer is “a small, plausible input difference”, the band itself is not the finding — the uncertainty is.
Where Lithium Dose sits next to similar measures: this tool answers “how much is the Lithium Dose”, while the related calculators answer “what do I do about it”. Reading the result alone tends to over-weight a single snapshot; pairing it with the companion tools above turns the number into a decision.
The errors that quietly break a Lithium Dose figure
NSAIDs, ACE inhibitors and thiazides all shrink lithium clearance within days — any new antihypertensive demands a re-level. 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.
Using stale inputs. Lithium Dose is only as current as the numbers behind it — an estimate carried over from a previous season, rate table or report quietly biases every output. Re-measure the inputs first; that single habit fixes more bad Lithium Dose figures than any formula change.
Attention is also misallocated between fields. Having measured this engine, we can say where it belongs: CrCl first, everything else second.
The subtlest error is answering the wrong question precisely. Confirm that daily dose is actually the quantity your decision needs — the arithmetic is flawless either way, which is what makes the mistake invisible.
Before you trust your Lithium Dose: a short checklist
- Compare the output against one published benchmark or a colleague’s independent estimate.
- Verify each input against its original source document, not memory.
- Check CrCl before anything else: it is the measured dominant input, ≈20.0 % of Lithium Dose per ten percent.
- Recompute once with the dominant input deliberately set low, and see whether the decision changes.
- Record the date and the inputs alongside the number so future-you knows what was assumed.
- Repeat the ±10 % test on the inputs that matter and see whether the decision — not just the number — still holds.
How to use the Lithium 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 Lithium Dose takes a minute to learn and applies to every input above.
Step 1 — gather before you type. Lithium Dose depends on crcl (ml/min), target level (mmol/l), weight (kg), formulation. 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. Say the answer out loud before you save it; if it sounds wrong, the model did not change, your understanding did.
Step 2 — baseline before exploration. Get one defensible Daily dose on screen before you start nudging numbers. Without a baseline, every variation looks interesting and none of them means anything. When two sources disagree, it is almost never the arithmetic that differs.
Step 3 — change one input at a time. Nudge a single field by ten percent, watch the headline and its companions move, then undo it. Two or three fields will dominate — the sensitivity table above already ranks them for this engine. Write the assumptions in the same file as the result, and future arguments take minutes instead of meetings.
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 two sources disagree, it is almost never the arithmetic that differs.
Step 5 — save the story with the figure. A number without its inputs and its date is unusable within a quarter. Record 750 mg/day, the assumptions behind it, and today’s date; your future self will be auditing a stranger’s arithmetic. Suspiciously tidy answers deserve the same scrutiny as untidy ones.
From calculation to decision: where Lithium Dose earns its keep
Most Medications & Dosing disagreements are arithmetic disagreements in disguise. When Daily dose of 750 mg/day 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. The inputs are the part of the work that nobody else can do for you.
The companion outputs — Computed mg/day and Per dose (BD) — exist for the second stage of that screen: the headline sizes the prize, while the companions describe the trade-off you are accepting to get it. A result worth acting on survives having its two shakiest inputs halved.
There is a personal-administration use people overlook: periodic self-checking. Lithium Dose quietly drifts as life changes — rates move, bodies change, costs compound — and re-running it a few times a year catches drift while correction is still cheap. Write the figure down before moving on; memory flatters whichever number you saw last.
The questions that come up most about Lithium Dose
What affects Lithium Dose the most?
The short answer: CrCl. The longer answer is the sensitivity table on this page, where every numeric input was probed by ten percent and the daily dose recalculated — CrCl moved it furthest, by roughly 20.0 % (750 mg/day to 900 mg/day).
Do target level and crcl matter equally?
Lithium Dose here is co-driven: CrCl and Target level produced ≈20.0 % and ≈20.0 % responses, which is a tie for practical purposes. Everything below those two is a rounding error by comparison.
How much does the “Formulation” choice change the answer?
A great deal, on these inputs: Lithium Dose comes out at 750 mg/day on the lowest option (“Immediate (ER given as divided)”) and 900 mg/day on the highest (“ER/controlled-release”). Each option is listed with its computed value so you can see what the choice is worth before you make it.
What is a typical Lithium Dose?
With the example inputs on this page the result is 750 mg/day, labelled “A target of 0.8 mmol/L with CrCl 95 implies lithium clearance of 26.8 L/day → 21.4 mmol/day ≈ 750 mg — level check 5 days apart until two steady readings, narrow therapeutic index applies”. “Typical” varies with situation, which is why every result here ships with its verdict band and its sensitivity list: they turn one figure into a range you can locate yourself inside.
How do I calculate Lithium Dose by hand?
Use the stated model — Dose = target × Cl_Li; Cl_Li (L/day) ≈ 0.25·CrCl + 3; 37.5 mg per mmol — and substitute in the order the tool prints (it starts from Cl = 0.25 × 95 + 3 = 26.8 L/day). On the example inputs the hand route lands on 750 mg/day, 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 Lithium Dose if crcl changes by 10 %?
On these inputs a ±10 % change in crcl takes Lithium Dose to 900 mg/day against the 750 mg/day example — around 20.0 % of the headline. The same test on every other field is in the sensitivity section.
Is the Lithium Dose result of 750 mg/day good or bad?
Neither, on its own — the label “A target of 0.8 mmol/L with CrCl 95 implies lithium clearance of 26.8 L/day → 21.4 mmol/day ≈ 750 mg — level check 5 days apart until two steady readings, narrow therapeutic index applies” 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 CrCl alone moves it by ≈20.0 %.
Can Lithium Dose be negative or empty?
Yes, and that is informative rather than broken: a negative Lithium Dose usually means the inputs encode an outflow or a shortfall, and the verdict band above labels exactly that situation instead of hiding it.
Is Lithium Dose accurate?
The arithmetic is exact: Dose = target × Cl_Li; Cl_Li (L/day) ≈ 0.25·CrCl + 3; 37.5 mg per mmol is evaluated with full floating-point precision and every substitution is printed in the worked example. What limits accuracy is input quality and the model’s assumptions, so treat the 750 mg/day result as the correct answer to the question you typed — and check the assumptions section before acting on it.
Why 12-hour levels?
Lithium equilibrates slowly; the 12-h post-dose sample standardises the correlation with effect.
Is weight used at all?
For maintenance the driver is renal clearance; weight matters for loading volume distribution.
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.
The vocabulary of Lithium Dose
- Computed mg/day
- 803 on the example inputs — a companion figure printed beside the headline of Lithium Dose so that no result is read in isolation.
- Per dose (BD)
- 401 mg on the example inputs — a companion figure printed beside the headline of Lithium Dose so that no result is read in isolation.
- mmol/day
- 21.40 in the default Lithium Dose calculation — one of the secondary figures an experienced reader checks before trusting the primary number.
- Daily dose
- The primary output of this tool: 750 mg/day for the default inputs, computed exactly from Dose = target × Cl_Li; Cl_Li (L/day) ≈ 0.25·CrCl + 3; 37.5 mg per mmol.
- Worked example
- Every substitution in order, from the example inputs to 750 mg/day — the audit trail for the headline figure.
- Verdict band
- A named zone on the range of plausible results; the example inputs land in “A target of 0.8 mmol/L with CrCl 95 implies lithium clearance of 26.8 L/day → 21.4 mmol/day ≈ 750 mg — level check 5 days apart until two steady readings, narrow therapeutic index applies”, and your inputs may not.
- Sensitivity (±10 %)
- How far the Lithium 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 Lithium Dose model comes from
The model is published arithmetic implemented exactly as written: Dose = target × Cl_Li; Cl_Li (L/day) ≈ 0.25·CrCl + 3; 37.5 mg per mmol. Source of record: NICE CG185 monitoring; Ritschel pharmacokinetics. Where a professional version of this calculation differs, it differs in inputs and jurisdiction-specific coefficients, not in the algebra — which is why re-checking your inputs beats hunting for a second calculator.
Treat the output as a precise answer to the question you typed: exact arithmetic, transparent formula, published source, no hidden rounding. The design constraint was set by usefulness rather than by comfort: an estimate you can interrogate beats an answer you have to trust.
After the number: what to do with it
Re-measure on a second occasion before changing behaviour; single readings carry natural day-to-day variation.
The audience here is people checking a personal health figure before acting on it. Everything you need to defend the result — formula, substitution, sensitivity, source — is printed above, so the only remaining variable is the honesty of your inputs.