Heparin Dose Calculator
The formula
What the ufh u/kg tells you
The weight-based unfractionated heparin protocol — bolus, infusion, and the aPTT nomogram steps that replaced empirical dosing.
Calculation: Raschke/UGB protocol: 80 U/kg bolus + 18 U/kg/h, aPTT-keyed step adjustments. Enter your inputs and every substitution is shown below the result.
Reading the result
aPTT reagent sensitivity is the hidden variable; the therapeutic range your lab printed is the one the protocol means.
Rules of thumb: Therapeutic aPTT 1.5–2.5× control ≈ 46–76 s most reagents
Limitations and best practice
The 1,000 U/h bolus cap that many protocols impose prevents the obesity-driven overshoot this arithmetic can create.
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 weight-based?
Anti-Xa instead of aPTT?
Source & methodology
Raschke 1993; UGB protocol.
Heparin 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. Searchers land on a Heparin Dose page for three reasons — to plan, to compare options, and to check that somebody else’s arithmetic is honest. This tool serves all three, and everything after the calculator explains the model instead of hiding it.
The number itself is the easy part. What takes judgement is knowing which inputs are facts in your situation and which are guesses wearing a decimal point — a distinction this page makes explicit for every field above.
Like most useful measures, Heparin Dose is a summary, and summaries hide as much as they reveal. The companion outputs and the input table are here to reopen what the headline compressed.
Nothing below is stock text pasted around a number: the worked example computes infusion rate = 1,260.0 U/h from this tool’s own defaults, and the sensitivity section ranks the inputs that move the result — Weight first, at ≈10.0 % 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 Heparin Dose calculation: formula and every input
One formula, published in full: Raschke/UGB protocol: 80 U/kg bolus + 18 U/kg/h, aPTT-keyed step adjustments. Anything you can read, you can reproduce in a spreadsheet, and that reproducibility is the whole point of printing it rather than hiding it behind a button.
Weight (kg) (example value 70) is a measured number in the unit named by the label; the formula does not convert for you. Stay in one unit system top to bottom; conversion rounding is where small errors enter.
Current aPTT (s) (example value 60) is a numeric input whose unit is fixed by the label; a wrong unit is a wrong answer wearing a plausible disguise. Replace the example with the figure from your own records — the tool recomputes instantly and the printed steps follow your numbers.
Therapeutic aPTT midpoint (s) (example value 62) 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.
First bolus needed? (0/1) (example value 1) 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.
Heparin Dose with real numbers, step by step
Rather than describe the calculation, here it is end to end — every substitution in order, starting from the inputs above. Starting figures: Weight (kg), Current aPTT (s), Therapeutic aPTT midpoint (s), First bolus needed? (0/1). The endpoint of that chain is 1,260.0 U/h of infusion rate, sitting in the “Weight-based start 1,260 U/h + 5,600 U bolus; aPTT 60 → protocol step 0% = 1,260 U/h” band.
- Start: 80 U/kg bolus, 18 U/kg/h
- = 5,600 U, 1,260 U/h
- aPTT 60 → 0% adjustment = 1,260 U/h
Starting bolus — 5,600.0 U. Read next to the headline, this is the figure that shows the shape of the trade-off.
aPTT ratio — 0.97. This is the number experienced users quote when the headline alone would mislead.
Daily U at this rate — 30,240.0. If your inputs change, this is usually the first companion figure to move.
Platelet watch — HIT risk days 4–14 — count q2–3d. This is the number experienced users quote when the headline alone would mislead.
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 Heparin Dose can reasonably move
The honest version of any estimate is a corridor, and this one is cheap to produce: Heparin Dose was recomputed at 5 points along the dominant input, with every other field left untouched.
| Weight setting | Infusion rate |
|---|---|
| 80 % of the example value | 1,008.0 U/h |
| 90 % of the example value | 1,134.0 U/h |
| example inputs | 1,260.0 U/h |
| 110 % of the example value | 1,386.0 U/h |
| 120 % of the example value | 1,512.0 U/h |
The corridor runs from 1,008.0 U/h to 1,512.0 U/h across that band — which is the range worth planning inside rather than the single 1,260.0 U/h point estimate. Reproduce it in the form above by editing Weight alone; the substitution steps will follow your figures exactly.
What actually moves your Heparin Dose
Nobody should have to guess which input matters. The engine was re-run once per field below — ten percent up, ten percent down, everything else frozen — and the results ranked by how far they moved the infusion rate. For Heparin 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.
- Weight: ten percent up gives 1,386.0 U/h, ten percent down gives 1,134.0 U/h — ≈10.0 % of the infusion rate either way
Weight is the dominant lever here: ten percent either way moves the result by about 10.0 %, from 1,134.0 U/h to 1,386.0 U/h. Measure that input from a document rather than from memory. The remaining fields can sit at safe defaults without materially changing the answer — knowing which is which is what separates a careful calculation from an anxious one.
What a Heparin Dose of 1,260.0 U/h means in practice
A number on its own is trivia; a number against a range is intelligence. On the example inputs the band reads “Weight-based start 1,260 U/h + 5,600 U bolus; aPTT 60 → protocol step 0% = 1,260 U/h”; 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 Weight, ±10 % covers 1,134.0 U/h to 1,386.0 U/h. The practical reading rules: read the band as a starting hypothesis, then test it: change the two dominant inputs by ten percent and see whether the verdict survives. Verdicts that survive stress are the ones worth acting on.
Where Heparin Dose sits next to similar measures: this tool answers “how much is the Heparin 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.
Why Heparin Dose results go wrong — and how to prevent it
The 1,000 U/h bolus cap that many protocols impose prevents the obesity-driven overshoot this arithmetic can create. 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.
Confusing a large number with an important one. Heparin Dose can be dominated by one input whose absolute value looks unimpressive, which is why this page ranks influence separately from magnitude.
This model has its own particular trap: Weight carries ≈10.0 % of the response per ten percent of error, so effort spent elsewhere is largely decorative.
Another is comparing across contexts: a Heparin Dose computed with one set of conventions should never be lined up against a figure computed with another. Check the inputs behind both before ranking them.
Heparin Dose verification checklist
- Re-run the calculation with a ±10 % stress on the two most sensitive inputs.
- Compare the result with one independent method or published benchmark.
- Re-verify Weight against a source document — ten percent of error there moves the headline by ≈10.0 %.
- Note the date and the inputs beside the number so the figure can be audited later.
- 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.
Step by step: getting a trustworthy Heparin Dose out of this tool
The tool does the arithmetic; the routine below is what makes the arithmetic trustworthy. Five steps, a minute total — and afterwards you will know not just what the number is, but which assumption produced it.
Step 1 — gather before you type. Heparin Dose depends on weight (kg), current aptt (s), therapeutic aptt midpoint (s), first bolus needed? (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. Say the answer out loud before you save it; if it sounds wrong, the model did not change, your understanding did.
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 Infusion rate (1,260.0 U/h for the example values), and note the verdict band. When in doubt, prefer the boring input: the interesting one is usually the one you misread.
Step 3 — isolate your variables. Change one field, observe, revert. The live sensitivity list does the ranking for the default inputs; verify it against your own, because dominance shifts when the starting point shifts. Comparisons are cheap: run the identical calculation for the alternative and look at the gap.
Step 4 — ask what would have to be true. Take the result you want and work backwards through the inputs until you find the assumption that produces it; then decide honestly whether that assumption is defensible. The inputs are the part of the work that nobody else can do for you.
Step 5 — write the one-line memo. “Infusion rate = 1,260.0 U/h on this date, from these inputs.” That line is the entire deliverable; everything else on this page is how you earned the right to write it. Write the figure down before moving on; memory flatters whichever number you saw last.
Where Heparin Dose matters in practice
Most Medications & Dosing disagreements are arithmetic disagreements in disguise. When Infusion rate of 1,260.0 U/h 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. When in doubt, prefer the boring input: the interesting one is usually the one you misread.
The companion outputs — Starting bolus and aPTT ratio — 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. Compare the calculation to the rough guess you arrived with, and ask why they differ.
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 Weight (kg) that nobody recalculated for a year. Numbers are cheap to produce and expensive to retract; the extra minute is the cheapest insurance available.
Quick answers: what searchers ask about Heparin Dose
What affects Heparin Dose the most?
The short answer: Weight. The longer answer is the sensitivity table on this page, where every numeric input was probed by ten percent and the infusion rate recalculated — Weight moved it furthest, by roughly 10.0 % (1,134.0 U/h to 1,386.0 U/h).
What is a typical Heparin Dose?
On the worked example above Heparin Dose comes out at 1,260.0 U/h. 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 Heparin Dose by hand?
Use the stated model — Raschke/UGB protocol: 80 U/kg bolus + 18 U/kg/h, aPTT-keyed step adjustments — and substitute in the order the tool prints (it starts from Start: 80 U/kg bolus, 18 U/kg/h). On the example inputs the hand route lands on 1,260.0 U/h, 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 Heparin Dose if weight changes by 10 %?
Try it in the form above and the printed substitution will follow you; the pre-computed answer for the defaults is 1,134.0 U/h to 1,386.0 U/h across the ten-percent probe, i.e. ≈10.0 % sensitivity on the infusion rate.
Is the Heparin Dose result of 1,260.0 U/h good or bad?
Good and bad are comparisons, so the honest test is three questions: where does your own Heparin Dose sit against the 1,260.0 U/h reference above, how far would a plausible input error move it (≈10.0 % per ten percent on Weight), and what does the alternative option compute to?
Does Heparin 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 Weight (kg) change materially.
Is Heparin Dose accurate?
The arithmetic is exact: Raschke/UGB protocol: 80 U/kg bolus + 18 U/kg/h, aPTT-keyed step adjustments 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 1,260.0 U/h result as the correct answer to the question you typed — and check the assumptions section before acting on it.
Why weight-based?
Mobin-Essad and Raschke showed fixed-dose heparin under-treated massively; U/kg cut sub-therapeutic time in half.
Anti-Xa instead of aPTT?
Anti-Xa monitoring avoids factor-deficiency and lupus-anticoagulant confounding — the modern first choice.
Do I need an account to use this Heparin Dose calculator?
No, and no data leaves the tab. The engine runs in the page itself, which is why the worked example, the bands and the sensitivity ranking all respond instantly to your keystrokes.
What the labels on this page mean
- Starting bolus
- 5,600.0 U for the Heparin Dose worked case; it sits next to the main result because it carries context the headline leaves out.
- aPTT ratio
- 0.97 on the example inputs — a companion figure printed beside the headline of Heparin Dose so that no result is read in isolation.
- Daily U at this rate
- 30,240.0 in the default Heparin Dose calculation — one of the secondary figures an experienced reader checks before trusting the primary number.
- Infusion rate
- The primary output of this tool: 1,260.0 U/h for the default inputs, computed exactly from Raschke/UGB protocol: 80 U/kg bolus + 18 U/kg/h, aPTT-keyed step adjustments.
- Worked example
- Every substitution in order, from the example inputs to 1,260.0 U/h — the audit trail for the headline figure.
- Verdict band
- The interpretation attached to a result (“Weight-based start 1,260 U/h + 5,600 U bolus; aPTT 60 → protocol step 0% = 1,260 U/h” on these inputs), which turns a bare number into a position on a scale.
- Sensitivity (±10 %)
- How far the Heparin Dose moves when a single input is nudged ten percent either way; the ranked list on this page is computed live from this engine.
The provenance of this Heparin Dose calculation
Everything above runs on one stated formula, applied without hidden coefficients: Raschke/UGB protocol: 80 U/kg bolus + 18 U/kg/h, aPTT-keyed step adjustments. Source of record: Raschke 1993; UGB protocol. 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.
This page is an estimation aid, not professional advice. The design rule is simple: two people entering identical figures must get identical answers. Nothing is smoothed, weighted or adjusted behind the scenes; where judgement enters, this page says so and names the input responsible.
Next steps after the calculation
Re-measure on a second occasion before changing behaviour; single readings carry natural day-to-day variation.
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.