Calculator
Percentage
Rate of Change
Loan Payment
Margin & Markup
Formulas
- Percentage: (value ÷ 100) × base
- Rate of change: (new − old) ÷ old × 100
- Margin: (price − cost) ÷ price × 100
Notes
- Results update as you type
- Loan uses equal principal + interest method
- Rate of 0% uses simple division
Related Tools
The calculator page bundles the four everyday calculations people reach for most — percentages, rate of change, loan payments and margin/markup — in one place. Results update as you type, and the formula behind each result is shown so you can verify it.
No app switching, no trying to remember whether margin divides by cost or by price.
How to use
- Percentage: enter a rate (%) and a base value to get "X% of base". Example: 15% of 200 = 30.
- Rate of change: enter a previous and current value to get the percentage change. Example: 80 → 100 is +25%.
- Loan payment: enter principal, annual rate (%) and term in months for the fixed monthly payment (amortized).
- Margin & markup: enter cost and sale price to see both margin and markup rates.
Common use cases
- Discounts & VAT
- Quickly check the final price after a big discount, or the tax on a net amount.
- Comparing loan terms
- Vary the rate and term to see how the monthly payment moves before talking to a lender.
- Pricing products
- Sanity-check the real margin of your current price, or work toward a target margin.
Good to know
The loan calculator uses standard amortization (equal monthly payments); at 0% interest it simply divides the principal by the term. Real loans vary with grace periods, prepayment and floating rates — confirm against your lender’s schedule.
Margin is based on price ((price − cost) ÷ price); markup is based on cost ((price − cost) ÷ cost). The two differ for the same numbers, so always be clear which one a conversation is about.
Frequently asked questions
What formula does the loan calculator use?
Standard amortization: M = P·r(1+r)ⁿ ⁄ ((1+r)ⁿ − 1), where r is the monthly rate and n the number of months. Early payments are mostly interest; later ones mostly principal.
Margin vs markup — what is the difference?
With cost 70 and price 100, margin is 30% ((100−70)÷100) while markup is about 42.9% ((100−70)÷70). Margin divides by price, markup divides by cost.
What does a negative change rate mean?
The value decreased. Going from 100 to 80 shows as −20%.
Can I rely on these results?
The formulas are standard, but institutions apply their own conditions to loans and taxes. For decisions with real money involved, double-check with the institution’s official calculation.