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Most popular
Your future, in clearer numbers
Make your money
make sense.
Free, thoughtful calculators for the decisions that shape your financial future. No sign-up. No jargon. Just useful answers.
✓ Free to use✓ Private by default✓ Clear assumptions
What would you like to work out?
Start with the decision
Useful financial planning begins with a better question.
ProsperMath is built for the moment before a financial decision, when you know the question but do not yet understand the trade-offs. How much must you save each month? What does a higher interest rate cost? Could a small annual fee materially change a long-term result? Each calculator turns one of those questions into assumptions you can see, change and compare.
The result is not a prediction or a recommendation. It is a reproducible estimate. We show the inputs, explain the calculation and identify important limitations so you can test more than one scenario before speaking to a provider, lender, tax authority or qualified adviser.
The toolkit
A calculator for every
money question.
Explore the numbers, compare paths and understand the trade-offs—without a spreadsheet in sight.
42 calculators shown
02
Compound Interest
See how time and regular contributions turn into long-term growth.Explore calculator →03
Dollar Cost Averaging
Project the outcome of investing a fixed amount consistently.Explore calculator →04
Lump Sum vs Monthly
Compare investing now with gradually investing over time.Explore calculator →05
Savings Goal
Find the monthly amount needed to reach a specific target.Explore calculator →06
Time to One Million
Estimate how long it could take to reach one million in your selected currency.Explore calculator →07
Investment Fee Impact
Reveal the long-term cost of annual investment fees.Explore calculator →08
CAGR
Calculate the smoothed annual growth rate between two values.Explore calculator →09
Inflation
Understand how rising prices affect future purchasing power.Explore calculator →10
Retirement Planner
Project your future pot and the income it might support.Explore calculator →11
Future Value
Calculate what money today and regular payments could become over time.Explore calculator →12
Present Value
Work out what a future amount is worth in today’s money.Explore calculator →13
Real Return
Measure investment growth after removing the effect of inflation.Explore calculator →14
Rule of 72
Estimate how long money could take to double at a fixed return.Explore calculator →15
ROI
Calculate net profit and return on investment after costs.Explore calculator →16
Annualised Return
Convert a total return over years and months into an annual rate.Explore calculator →17
Mortgage vs Investing
Compare overpaying a mortgage with investing the same monthly cash.Explore calculator →18
Pay Off Debt vs Invest
Compare a predictable debt saving with an assumed investment return.Explore calculator →19
Pension Tax Relief
Estimate relief at source and possible additional UK pension relief.Explore calculator →20
Dividend Income
Estimate annual and monthly income from a portfolio and yield.Explore calculator →21
Dividend Reinvestment
Project growth when dividends are reinvested rather than withdrawn.Explore calculator →22
Retirement Withdrawal
Estimate how long a pot could support inflation-linked withdrawals.Explore calculator →23
Coast FIRE
See whether current investments could coast to a retirement target.Explore calculator →24
FIRE Number
Estimate the portfolio needed to support annual spending.Explore calculator →25
Mortgage Overpayment
Estimate the interest and time saved by regular overpayments.Explore calculator →26
Loan Overpayment
Calculate repayments and the effect of paying extra each month.Explore calculator →27
Mortgage Payment Change
Estimate how a new interest rate could change your monthly payment.Explore calculator →28
Refinance Break-even
Find when lower mortgage payments could recover switching costs.Explore calculator →29
Emergency Fund
Set a cash-buffer target and estimate when you could reach it.Explore calculator →30
House Deposit
Calculate a deposit or down-payment target and saving timeline.Explore calculator →31
Credit Card Payoff
Estimate payoff time and interest from a fixed monthly payment.Explore calculator →32
Balance Transfer
Compare a promotional transfer with keeping your current card.Explore calculator →33
Avalanche vs Snowball
Compare two popular ways to prioritise multiple debts.Explore calculator →34
Cost of Waiting to Invest
See the potential long-term effect of delaying your investment plan.Explore calculator →35
United Kingdom
ISA Allowance 2026/27
Track subscriptions against the £20,000 adult ISA allowance.Explore calculator →36
United Kingdom
UK Dividend Reinvestment
Compare ISA reinvestment with a taxable account under 2026/27 rules.Explore calculator →37
United States
401(k) Employer Match 2026
Estimate contributions, employer match and remaining deferral room.Explore calculator →38
Canada
TFSA Contribution Room 2026
Estimate remaining room using your opening amount and contributions.Explore calculator →39
Australia
Super Contribution Cap 2026/27
Check concessional contributions against the annual cap.Explore calculator →40
New Zealand
KiwiSaver Calculator 2026
Estimate employee, employer and government contributions.Explore calculator →41
Income
Salary Increase & Pay Rise
Calculate a raise by year, month and paycheck, then compare it with inflation.Explore calculator →42
Savings
Savings Interest
Compare savings rates, regular deposits, interest tax and inflation.Explore calculator →43
Interest-only
Interest-Only Overpayment
See how lump-sum and monthly capital payments could reduce the balance and interest.Explore calculator →44
New comparison
Reduce Term vs Payment
Compare shortening the mortgage with lowering the payment after a lump sum.Explore calculator →45
Budgeting
Sinking Fund
Plan monthly savings for annual bills, repairs, holidays and other known costs.Explore calculator →46
Budget audit
Subscription Cost
Turn recurring subscriptions into annual and multi-year costs.Explore calculator →47
Personal balance sheet
Net Worth
Add up assets and debts to estimate net worth and liquid net worth.Explore calculator →48
Financial progress
Savings Rate
Calculate the share of income going to saving, investing and extra debt payoff.Explore calculator →49
UK property tax
Stamp Duty Calculator
Estimate SDLT on a home, first purchase, buy-to-let or second property.Explore calculator →50
US retirement
RMD Calculator 2026
Estimate a required minimum distribution from an IRA or retirement account.Explore calculator →51
US income
Overtime Pay & Tax
Estimate overtime gross pay and what may remain after simple tax assumptions.Explore calculator →Try it now
Investment Growth Calculator
See how an investment could grow after contributions, fees and inflation.
Projected value
£0
View year-by-year breakdown ＋
| Year | Contributions | Growth | Balance |
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Numbers with context
A result you can examine—not a black box.
A useful calculator should make it easier to think, not create false certainty. Our shared approach is designed around three questions.
What does the result mean?
Every tool begins with a plain-language outcome and a breakdown of the amounts behind it. Growth tools separate money contributed from estimated growth. Borrowing tools distinguish principal, interest and time. Comparison tools apply the same starting assumptions to both paths.
Which assumptions matter?
Rates, timeframes, fees, inflation and contribution timing can materially change an answer. Inputs remain visible and editable so you can compare a cautious case with a central and optimistic case instead of treating one attractive result as inevitable.
What is outside the model?
Markets move unevenly, variable rates change, taxes depend on individual circumstances and financial products contain their own rules. Calculator pages state the main omissions and link to official sources when tax-year or regional limits are involved.
How ProsperMath publishes
Worked examples, visible formulas and review dates.
Guides are prepared by the ProsperMath Editorial Team, checked against the connected calculator and supported with official sources where appropriate. We do not invent professional credentials, recommend specific products or accept payment to alter a calculation.
Errors and unclear assumptions can be reported through our contact page. Material corrections are made in the calculator or guide rather than hidden behind a disclaimer.
Read our editorial standards →Read the calculation methodology →Practical guides
Understand the decision behind the number.
Savings
How Much Interest Will $10,000 Earn in a Year?
Compare APY or AER while allowing for deposits, tax and inflation.
Read guide →SavingsAPY vs Interest Rate: What Actually Changes?
Understand nominal rates, compounding and effective annual returns.
Read guide →InvestingWhat Is Your Return After Fees and Inflation?
Move from a headline return to a more realistic planning figure.
Read guide →PropertyReduce the Mortgage Term or Lower the Payment?
Compare both outcomes after making the same lump-sum overpayment.
Read guide →DebtHow Much Extra Should You Pay on a Credit Card?
Compare payoff time and interest before choosing a sustainable amount.
Read guide →PropertyCan You Overpay an Interest-Only Mortgage?
Understand the effect on capital, monthly interest and the term-end balance.
Read guide →