Savings & Investment Calculators
Eight calculators for money you are growing rather than borrowing — compounding, targets, returns and the quiet drag of inflation.
Compounding is the whole game
The difference between simple and compound interest looks trivial in year one and enormous in year twenty. Simple interest is charged on the original principal only; compound interest is charged on the balance including previous interest, so growth accelerates. Compare the two directly with the Simple Interest and the Compound Interest — same inputs, very different endings.
Goal-first or growth-first?
There are two ways to plan. Growth-first asks “what will this become?” — that is the Compound Interest and the Retirement. Goal-first asks “what do I need to put in?” — that is the Savings Goal, which works backwards from a target and a date to a monthly contribution. Most people find the second more useful, because it produces an action rather than a number.
Before any of it, the buffer
Growth plans assume you never have to sell in a hurry. That assumption holds only if there is accessible cash behind it, which is what the Emergency Fund Sizer sizes — a months-of-cover figure built from your outgoings, job security, dependants and sick pay rather than the usual three-to-six-month range. Money above that target is what belongs in the tools on this page; money below it does not.
Measuring what you already did
For a completed investment, the ROI Calculator gives the plain percentage return, and the Investment Return gives the annualised rate (CAGR) — the figure that lets you compare an eighteen-month holding against a five-year one. A 40% total return over five years is a very different investment from 40% in one year, and only the annualised figure makes that visible.
Do not forget inflation
A projection in today's money is optimistic by definition. The Inflation Calculator converts a future sum back into present-day purchasing power, which is the honest way to read any long-range retirement or savings projection. As a rule of thumb, subtract inflation from your assumed growth rate before you decide whether a plan works.
Where the money sits matters as much as the rate
Two accounts paying the same headline rate can leave you with different amounts, because tax and compounding frequency both bite. Interest paid monthly and left in place compounds twelve times a year rather than once, which lifts the effective rate slightly above the quoted one; interest paid away as income does not compound at all. Tax status matters more: in the UK, interest inside an ISA is untaxed, while interest outside one counts against your personal savings allowance and then attracts income tax at your marginal rate. Work out that marginal rate with the income-tax-calculator before comparing a tax-free rate against a taxable one — a 4% tax-free account beats a 5% taxable one for a higher-rate taxpayer. None of the calculators here apply tax automatically, so treat every projection as a gross figure and discount it yourself.
Frequently asked questions
Should I pay off debt or save first?＋
Compare the two rates honestly. Debt interest is a guaranteed cost; savings growth is an expected return. If a credit card charges 22% and a savings account pays 4%, clearing the card is worth far more than saving, and the gap is certain rather than hoped for. The usual exceptions are keeping a small emergency buffer in cash so a surprise does not put you straight back on the card, and any employer pension match, which is an immediate return no debt rate beats.
What growth rate should I assume in a projection?＋
There is no correct number, which is why the calculators let you set it. A common convention is to model a diversified equity portfolio at 5–7% nominal per year and cash at whatever the account currently pays, then run the same projection again two percentage points lower to see how sensitive the plan is. If the plan only works at the optimistic rate, it is not a plan.
Why does my real return look so much worse than the headline?＋
Because two things are subtracted from it that the headline ignores: inflation and charges. A 6% return with 2.5% inflation is 3.5% in purchasing power, and a 1% platform-and-fund charge takes roughly a fifth of what is left. Run the result through the inflation calculator before deciding whether a projection is comfortable.
Do these calculators account for tax?＋
No. Every figure is gross. Tax treatment depends on the wrapper the money sits in and on your marginal rate, both of which vary by person and by country, so applying a rate automatically would be wrong more often than right.
More finance & money tools
Every tool listed here produces an estimate from the numbers you enter and the assumptions stated on its own page. None of them accounts for fees, charges, tax treatment or your individual circumstances, and rates and thresholds change. Tool Corner is not authorised by the Financial Conduct Authority and does not give financial advice. Speak to a qualified adviser before making a financial decision.
Each tool states its own assumptions and sources. Read the full disclaimer.