MPC from MPS calculator
Find how much of extra income gets spent: a household that saves 0.2 of each extra unit of disposable income spends 0.8, because the shares saved and spent always add up to 1. Free in your browser.
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Run — free
Worked example
- Mps
- 0.2
- Mpc
- 0.8
The marginal propensity to consume measures how much of an extra unit of disposable income a household spends rather than saves. In the simple closed-economy identity used throughout principles of macroeconomics, every dollar of additional income is either consumed or saved, so the marginal propensity to consume plus the marginal propensity to save equals one. Rearranging that identity gives the workhorse formula MPC equals one minus MPS. Students use it when a problem states the saving rate out of income and asks for the consumption response; instructors and LMS platforms need the same deterministic answer for grading; analysts converting survey-based saving propensities into consumption multipliers rely on the same one-step complement. This calculator accepts a single MPS value between zero and one inclusive, returns MPC with a clear formula string, and rejects fractions outside that interval so clients never get a nonsense share.
What MPC and MPS mean and why they sum to one
Marginal propensity to consume (MPC) is the change in consumption divided by the change in disposable income: the fraction of an extra unit of income that is spent on goods and services. Marginal propensity to save (MPS) is the complementary fraction that is saved. In the simplest Keynesian consumption function, households allocate every extra unit of disposable income to either consumption or saving, with no third residual in the accounting identity used in introductory models.
That bookkeeping identity is written MPC plus MPS equals one. If a household saves twenty cents of every extra dollar, it spends eighty cents, so MPS equals zero point two and MPC equals zero point eight. If it saves nothing, MPS is zero and MPC is one; if it saves everything, MPS is one and MPC is zero.
Intermediate values fill the unit interval. The identity is an accounting statement about how income is split at the margin, not a behavioral theory of why people save. Real economies also include taxes, transfers, and imports that affect multipliers, but the MPC–MPS complement remains the first step before those extensions.
This capability implements only that first step: given MPS, return MPC equals one minus MPS. It does not estimate elasticities from micro data, forecast consumption paths, or compute the Keynesian spending multiplier one over one minus MPC.
Where an MPC-from-MPS calculator earns its keep
Introductory macroeconomics courses assign MPC and MPS problems because the complement identity underpins the simple spending multiplier and the slope of the consumption function. Tutoring sites and LMS plugins need a deterministic oracle that rejects out-of-range propensities instead of silently returning negative or above-one shares that a buggy grader might accept.
Policy and forecasting notebooks that start from a published household saving rate often convert that rate into an MPC before chaining multiplier or IS-curve sketches; a single validated call avoids off-by-one transcription errors when analysts flip between percent and fraction notation. Pair this capability with separate tools when you need the multiplier itself or income–consumption tables; keep this surface focused on the one-minus identity that turns a saving propensity into the fraction of extra income spent.
What you can do with it
Multiplier and macro notebook prep
Convert a published or survey-based saving propensity into MPC before computing spending multipliers in analysis notebooks.
FAQ
What is the formula for MPC from MPS?
The calculator returns that complement plus a short formula string when MPS is a finite fraction in [0, 1].
Why must MPS be between 0 and 1?
MPS is a share of extra disposable income saved.
Does this tool compute the spending multiplier?
No. It only returns MPC from MPS. The simple multiplier 1/(1−MPC) is a separate step you can apply in your own notebook or with another calculator.
What does an MPC of 0.8 mean?
It means that of each extra unit of disposable income, 0.8 is spent on goods and services and the remaining 0.2 is saved. It describes how income is split at the margin, not why people save.
What if a household saves nothing?
Then the propensity to save is 0 and the propensity to consume is 1: every extra unit of income is spent. At the other end, saving everything gives a propensity to consume of 0.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/econ/mpc-from-mps \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"mps":0.2}'const res = await fetch("https://api.kit.forhosting.com/econ/mpc-from-mps", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"mps": 0.2
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/econ/mpc-from-mps",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"mps": 0.2
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/econ/mpc-from-mps", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"mps":0.2}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"mps":0.2}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/econ/mpc-from-mps", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"mps": 0.2
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "econ.mpc_from_mps",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
What MPC and MPS mean and why they sum to one
Keep those applications in your notebook; use this endpoint when you need a reproducible complement of a validated saving propensity.
Inputs, outputs, validation, and how to call the calculator
The value must lie in the closed interval from zero to one inclusive. Negative values are rejected because a saving share cannot be less than zero in this definition; values greater than one are rejected because they would imply spending a negative share of income. Numeric strings that parse to finite numbers in range are accepted so form posts and spreadsheet exports work without an extra cast. Example: mps equals zero point two yields mpc equals zero point eight; mps equals zero point three five yields mpc equals zero point six five. POST a JSON body with one required finite number: mps, the marginal propensity to save expressed as a fraction of extra disposable income. Missing fields, empty strings, non-numeric text, Infinity, and NaN all fail with invalid_input naming the field. On success the response echoes mps (rounded for stable goldens), returns mpc as one minus mps with the same stable rounding, and includes formula set to MPC = 1 − MPS. The browser tool is free for interactive checks; successful API calls use prepaid KIT balance at $0.002 per item, and failed validation is not billed.
Where an MPC-from-MPS calculator earns its keep
Because every successful call stays cheap at $0.002 with no large language model in the path, you can wire the endpoint into bulk homework generators without worrying about token budgets.
Integration use cases
Homework and exam MPC checks
Students enter MPS from a problem set and verify MPC = 1 − MPS against textbook keys and multiplier warm-up questions.
LMS and tutoring auto-grading
Score marginal propensity items with a deterministic oracle that rejects MPS outside [0, 1] as invalid_input.
Technical questions
Does MPC plus MPS always equal one?
In the simple Keynesian identity used here, yes: every extra unit of disposable income is either consumed or saved, so MPC + MPS = 1 by construction.
What does the MPC from MPS calculator cost?
The browser tool is free. API requests use prepaid KIT balance at $0.002 per successful call; invalid input is not billed.