Why this site exists
Exponential growth and decay describe an unusually wide range of real processes: money compounding in an account, bacteria dividing in a petri dish, a virus spreading through a population, a radioactive isotope losing atoms, a population expanding toward a resource ceiling. Most calculators online cover exactly one of these, built by a different team with a different formula and a different notation for the same underlying math. This site instead treats them as one problem: a single exponential engine, x(t) = x₀ × (1 + r)^t and its continuous twin x(t) = x₀ × e^(kt), wired into 22 focused pages so each scenario gets its own inputs, its own worked examples and its own plain-language explanation without re-deriving the math from scratch every time.
How the calculators work
Every calculator on the site shares the same small set of underlying functions for discrete growth, continuous growth, doubling time and half-life, defined once in the codebase and reused everywhere. A compound interest calculation and a bacterial growth calculation are, mathematically, the same formula with a different label on the rate and a different name for the time unit. Centralizing the math this way means a fix or accuracy improvement made in one place benefits every page instantly, rather than needing to be repeated 22 times with 22 chances to introduce an inconsistency.
Accuracy
All calculations run in JavaScript using the browser's IEEE-754 double-precision arithmetic. Standard library functions Math.pow, Math.exp and Math.log handle every operation, the same functions used by scientific and financial software elsewhere. Results are exact to roughly 15 significant digits, well beyond what any real-world input justifies, and every worked example published on the site is checked by hand against the same closed-form formula displayed next to it so the text and the interactive tool never disagree.
Who this is for
Students checking a homework answer, developers who need a quick sanity check on a formula before writing it into code, analysts comparing CAGR across two investments, and anyone curious how fast a number actually grows at a given rate all use these pages the same way: type a number, read the answer, move on. Nothing requires a login, a download or a spreadsheet.
Privacy
No calculator input is ever sent to a server. Every result is computed locally in your browser. See the full privacy policy for what limited site-traffic analytics are collected separately from calculator use.
Performance
The site ships pre-rendered static HTML, self-hosts its own fonts and defers non-critical JavaScript so the page is interactive before a chart library ever loads. Lighthouse audits target 95+ on both desktop and mobile.
Coverage
The 22 supporting pages cover compound interest, population growth, bacterial growth, viral spread, drug metabolism, radiocarbon dating, logistic curves, regression, equation solving and pure mathematical reference, alongside the main exponential growth calculator on the homepage. Start at the homepage, browse the worked examples, or get in touch with a question or a formula that is missing.
Design principles
Three rules guide every page on this site. First, every number shown is either directly computed from your input or independently verified by hand against the closed-form formula next to it, never an approximation dressed up as an exact answer. Second, every calculator updates as you type or drag a slider, with no submit button and no page reload, because the entire point of an interactive tool is removing the friction between asking a question and seeing the answer. Third, the explanation around each calculator is written to answer the question directly in the first sentence, then build out the supporting detail, rather than burying the useful part under paragraphs of preamble.
What this site does not do
This is not financial, medical or legal advice. The compound interest and investment calculators model the mathematics of compounding; they do not account for taxes, fees, inflation or the fact that real investment returns are rarely a single constant rate. The half-life and drug decay calculators model first-order elimination kinetics; they are not a substitute for a pharmacist or physician's dosing guidance. Every calculator here answers "what does this formula predict," not "what will actually happen in your specific situation," and the FAQ on each page tries to be explicit about that boundary.
How the site is built
The site is a statically generated React application: every page is pre-rendered to plain HTML at build time, so a visitor's first request returns a complete, readable page before any JavaScript runs, and the calculators become interactive a moment later once the page hydrates. This keeps the site fast on slow connections and older devices, and it means the core content of every page, including the FAQ answers and worked examples, is available even if JavaScript fails to load for any reason.
Feedback and corrections
If a formula, a worked example, or a piece of wording anywhere on the site looks wrong, that is worth reporting. Every published number is meant to be independently checkable against the formula shown beside it, and a mismatch is a bug worth fixing rather than a rounding quirk to shrug off. Use the contact form with the specific page and the input values you used, and it will be looked at directly rather than routed through a generic support queue.
Language coverage
The homepage is fully translated into 14 additional languages, covering the primary calculator, its inputs and its explanatory text. The 22 supporting calculators below it, covering compound interest, decay, half-life and the rest, remain English-only for now; each still works identically in every browser and every locale, since the underlying math and the calculator itself do not depend on language. Expanding full translation to every supporting page is a larger undertaking than translating a single homepage, and it is being done deliberately rather than machine-translated all at once to keep the worked examples and FAQ answers accurate rather than merely fluent.