Every CalcsMaster calculator uses a standard, published formula. This page lists what each one does and the assumptions behind it, so you can check a result yourself or decide whether it fits your situation.
The Basics
Calculated in your browser. The numbers you enter stay on your device. They are not sent to our servers or stored.
Estimates, not advice. Results use the rates and values you enter. Real returns, rates, fees and tax rules differ, so treat every result as an estimate and confirm important figures with your lender, bank, employer or a qualified professional.
No taxes, fees or inflation unless stated. Results are before tax and charges. The Inflation Calculator is the only one that adjusts for inflation.
Rounding is for display only. Calculations run at full precision and are rounded only when shown.
Formulas and Assumptions by Calculator
| Calculator | Formula or method | Key assumptions |
|---|---|---|
| Loan EMI | EMI = P × R × (1+R)ⁿ ÷ [(1+R)ⁿ − 1] | R is the annual rate ÷ 12. Interest is charged on the outstanding balance (reducing balance). Fees and insurance are not included unless you enter them. |
| UK Stamp Duty | Sum of (slice of the price in each band × band rate) | Stamp Duty Land Tax for England and Northern Ireland from 1 April 2025: first-time buyer relief up to 500,000, +5% for additional properties from 40,000, +2% for non-UK residents. Scotland and Wales are not covered. |
| Loan Comparison | The same EMI formula for each option | Differences in fees and prepayment rules are not modelled. |
| SIP | FV = P × [((1+i)ⁿ − 1) ÷ i] × (1+i) | Investments happen at the start of each period. i is the annual rate divided by the number of periods per year. The return is constant. |
| Mutual Fund | SIP formula above, or FV = P × (1+r)ⁿ for a lumpsum | Constant yearly return. Fund charges and taxes are not deducted. |
| SWP | Monthly: balance × (1 + monthly rate) − withdrawal | Monthly rate = (1 + annual rate)^(1/12) − 1. Growth is added first, then the withdrawal is taken at month end. The withdrawal does not rise with inflation. |
| Fixed Deposit | M = P × (1 + R ÷ n)^(n × T) | n is the compounding frequency you choose (yearly by default). Interest is paid at maturity. |
| Interest | Simple: P × R × T. Compound: P × (1 + R ÷ n)^(n × T) | Constant rate. No fees or tax. |
| PF and SSY | Compound growth on regular deposits | Scheme rates change over time. The rate you enter is used for the whole period. SSY deposits are made at the start of each year for 15 years, and interest is added once a year, rounded to the nearest whole currency unit, for 21 years. Default rates, checked 23 October 2026: EPF 8.25% for FY 2025–26, PPF 7.1% and SSY 8.2% for the October–December 2026 quarter. Update the rate field when they change. |
| 401(k) | Each month: balance × (1 + r ÷ 12) + contributions | Contributions are a percentage of salary, salary rises once a year, and the legal contribution limit is not applied (the 2026 IRS employee limit is $24,500, plus catch-up; the US Paycheck calculator does apply it). |
| Inflation | Future cost = amount × (1 + inflation)ⁿ | A constant yearly inflation rate that you choose. It is an assumption, not a forecast. |
| CAGR | Internal rate of return of the cash flows you enter. With one amount at the start and one at the end it equals the plain CAGR, (end ÷ start)^(1 ÷ years) − 1. | Cash flows occur at yearly intervals, in four phases: yearly investments, a waiting period, yearly payouts and a final maturity amount. |
| GST and VAT | Add: net × (1 + rate). Remove: gross ÷ (1 + rate) | One flat rate. Exemptions and mixed rates are not handled. |
| Percentage and Discount | Percent of: Y × X ÷ 100. Change: (new − old) ÷ |old| × 100 (undefined when the old value is 0). Sale price: price × (1 − discount) | A second discount applies to the already discounted price. Tax is applied after discounts. |
| Hourly to Salary | Annual = hourly rate × hours per week × weeks per year | Results are gross pay, before tax. Overtime and bonuses are not included. |
| US Sales Tax | Tax = price × (state rate + local rate). Remove: total ÷ (1 + rate) | State rates and average local rates from the Tax Foundation (1 July 2026). Real local rates depend on the address. One rate is applied to the whole price; exemptions are not handled. |
| Canada Sales Tax | Tax = price × (federal rate + provincial rate). Remove: total ÷ (1 + rate) | GST, HST, PST, RST and QST rates for 2026. QST is charged on the pre-tax price. Zero-rated and exempt items are not handled. |
| US Paycheck | Net = gross − pre-tax deductions − federal income tax − Social Security (6.2% up to 184,500) − Medicare (1.45%, +0.9% withheld above 200,000) − state tax | 2026 federal brackets and standard deductions from IRS Rev. Proc. 2025-32. The 401(k) is limited to 24,500 a year and deductions cannot exceed pay. State tax is one flat rate you choose. Credits, other income and extra withholding are not included. |
| Tip | Tip = bill × tip %. Per person = (bill + tip) ÷ people | Tip is calculated on the amount you enter. |
| Time, Time Card, Age | Time is converted to minutes (or seconds), added or subtracted, then converted back. Age counts whole years, months and days; if the start day does not exist in a month (for example 31 January or 29 February) it counts as the last day of that month. | Calendar months and leap years are respected, and the end date is not counted when you count days between dates. Business days can treat Saturday & Sunday, Friday & Saturday, or Sunday only as the weekend. |
Testing and Corrections
When we build or change a calculator, we compare its results with independent calculations of the same formula. If you find a result that looks wrong, please tell us at [email protected] or through the contact page, with the values you entered. We correct confirmed errors, and the "Last updated" date on each page shows when it was last changed in a way that matters to visitors.
Who Publishes This Site
CalcsMaster is an independent publisher of free calculators. Read more on the About page. Our calculators do not collect your personal or financial data, and we do not sell financial products.