Do the maths before you sign anything
Thirteen calculators for the money decisions you make for yourself — a mortgage, a loan, a pay offer, a split restaurant bill. Each one turns a headline number into the figure that actually matters, and every calculation runs in your browser.
The short answer
A personal money decision is easier to get right when you can see the whole number, not the headline one. A loan's real cost is its total interest over the full term, not its monthly payment; a salary is only comparable once every offer is converted to the same pay period; a split bill only comes out even when the per-person shares are forced to sum to the exact total. These calculators do that arithmetic — mortgage and loan repayment, compound growth and doubling time, salary conversion, sales tax, discounts and bill-splitting — so the figure you act on is the one you'd have reached with a spreadsheet and an hour.
Before you borrow
loans and mortgagesA loan's true cost is never just the headline interest rate — it's the total you repay over the full term, plus the tax, insurance and PMI a lender bundles in. Run the numbers before you sign anything.
Grow your money
saving, investing, doubling timeTwo calculators for the other side of the ledger — what your money does for you rather than what it costs you.
Your pay, in every direction
salary, hours, take-homePay gets quoted in whatever period suits whoever's quoting it. Converting cleanly between periods is the first step in comparing two offers.
Everyday money math
tax, discounts, splitting a billThe small, frequent calculations — a discount at the till, a group bill, sales tax added or removed — where doing it in your head is where the rounding errors and the arguments start.
The monthly payment is not the cost
Almost every borrowing decision gets made on the monthly payment, because that's the number the lender leads with. It's the wrong number to decide on. Two loans with the same monthly payment can differ by tens of thousands over their lives if one runs longer, and a lower monthly payment usually buys that comfort by stretching the term and adding interest.
The Mortgage Calculator and Debt Repayment Calculator both surface the figure that actually matters: total interest and total cost over the full term. Look there first, then at the monthly number to check it fits your budget — not the other way round.
The EMI Calculator adds one distinction worth understanding: Reducing Balance versus Flat Rate. Flat-rate interest is charged on the original amount for the whole term, so the same quoted rate costs you noticeably more than a reducing-balance loan, where interest is charged only on what you still owe. If a lender quotes a flat rate, the tool lets you see what it really works out to.
How much you can borrow is a different question
"What will this cost?" and "how much can I actually get?" are two separate calculations, and confusing them is how people end up house-hunting in the wrong bracket. Cost runs from a loan amount you already have in mind. Affordability runs the other way — from your income and existing debts back to the largest loan those figures will support.
The Loan Affordability Calculator works from your debt-to-income ratio (DTI): your gross monthly income and existing debt payments set a ceiling, and the tool returns the maximum loan, monthly payment and purchase price that stay under it. It's the number to establish before you fall for a specific property, not after.
On a mortgage specifically, the Loan-to-Value (LTV) Ratio Calculator adds the other constraint lenders care about. LTV is simply loan ÷ value × 100, and the threshold to remember is 80%: borrow more than 80% of the property's value and you're typically required to pay PMI on top. Knowing where your down payment puts you on that line tells you whether finding a little more up front removes a monthly charge entirely.
- 1Budgeting from the monthly payment alone
A payment you can meet this month says nothing about what the loan costs across its life, or whether the term is quietly doing the work. Check total interest before you commit.
- 2Ignoring the 80% LTV line
A down payment that lands you at 81% LTV can mean paying PMI that a slightly larger deposit would have avoided outright. It's worth calculating exactly where you fall.
Growth, and the shortcut for it
The Compound Interest Calculator projects what a balance becomes over time: pick a compounding frequency from annual up to continuous, add optional monthly contributions, and read the year-by-year table. It's the precise answer. The Rule of 72 Calculator is the mental-math version of the same question — years to double ≈ 72 ÷ rate% — and it shows the exact logarithmic answer beside the estimate, plus how the Rule of 70 and Rule of 69.3 compare.
Use the Rule of 72 to sanity-check a claim in your head — 6% doubles your money in roughly twelve years — and the compound-interest tool when you need the real figure with contributions folded in.
The everyday arithmetic that trips people up
Small calculations go wrong in specific, repeatable ways. The Hours Calculator handles one of them: a shift that crosses midnight. A naive subtraction of 06:00 from 22:00 gives a negative number; the tool handles the day rollover, so an overnight shift comes out as eight hours rather than nonsense. The Salary Calculator handles another — converting one pay rate into annual, monthly, bi-weekly, weekly, daily and hourly equivalents at once, using your actual hours and paid leave, so two offers quoted in different periods finally sit on the same axis.
- Bill
- $100.00 split three ways
- Naive maths
- 100 ÷ 3 = $33.33 each
- Three shares
- 33.33 × 3 = $99.99 — a cent short
- The fix
- One person pays $33.34, the shares sum to exactly $100.00
The Split Bill Calculator does this for you — cent-accurate shares that always add back up to the total, after tax, tip and any discount.
For prices themselves, the Sales Tax & VAT Calculator adds or removes tax, VAT or GST at any rate you enter, and — importantly — can work backwards from a gross price to the pre-tax figure. The Percent Off Calculator gives you a sale price and the amount saved in one step, while the Discount & Markup Calculator covers the harder cases with five modes: markup, margin, discount, reverse discount, and stacked discounts, where a "20% off, then a further 10%" is a 28% discount, not 30%.
Which one do I want?
Several tools here overlap. The short version:
| mortgage-calculator vs loan-affordability-calculator | You have a price in mind and want to know what it will cost — full PITI payment and lifetime interest. | You want the reverse: the largest loan your income and existing debts will actually support. |
|---|---|---|
| emi-calculator vs debt-repayment-calculator | Comparing loan offers, weighing Reducing Balance against Flat Rate, or modelling lump-sum prepayments. | Tracking a single debt's payoff timeline and seeing how one extra monthly payment shortens it. |
| compound-interest-calculator vs rule-of-72-calculator | You need the precise future value, with contributions and a chosen compounding frequency. | You want a quick doubling-time estimate you can do in your head and check against the exact answer. |
| percent-off-calculator vs discount-markup-calculator | A single percentage off a price — sale price and savings, done. | Anything harder: margin versus markup, reverse discounts, or two discounts stacked together. |
Why this set
Total interest over a loan's life, a salary on a comparable footing, a bill split to the exact cent — each tool surfaces the figure a lender or a menu would rather you didn't do in your head.
Income, debts, prices and pay all run client-side. Nothing you type is uploaded, so it's reasonable to use your real numbers rather than round ones.
Borrowing, growth, pay and everyday tax and discounts each get a purpose-built calculator, with a comparison table for the cases where two of them overlap.
Questions
Should I decide on a loan by its monthly payment?
No — the monthly payment is the number lenders lead with, but it hides the total cost. Two loans with the same payment can differ by tens of thousands over their lives if one runs longer. Check total interest and total cost over the full term first, using the mortgage or debt-repayment calculator, then confirm the monthly figure fits your budget.
What's the difference between the mortgage and loan-affordability calculators?
The mortgage calculator answers "what will this cost?" from a loan amount you already have in mind, returning the full PITI payment and lifetime interest. The affordability calculator runs the other way: from your gross income and existing debts, using your debt-to-income ratio, it returns the largest loan you can actually carry. Establish affordability first, then price a specific property.
When does PMI apply to a mortgage?
PMI is typically required when your loan-to-value ratio is above 80% — that is, when you borrow more than 80% of the property's value. The loan-to-value calculator shows exactly where your down payment puts you on that line, so you can see whether finding a little more up front removes the charge entirely.
How accurate is the Rule of 72?
It's a mental-math estimate: years to double is roughly 72 divided by the interest rate percent. It's close enough to sanity-check a claim in your head, and the Rule of 72 calculator shows the exact logarithmic answer next to it — along with the Rule of 70 and Rule of 69.3 and each one's error — so you can see how far off the shortcut is at your rate.
Why doesn't a bill always split evenly?
Because division leaves a remainder. Splitting $100.00 three ways gives $33.33 each, and three lots of $33.33 come to $99.99 — a cent short. The split-bill calculator forces the per-person shares to sum to the exact total, assigning the odd cent to one person, so the group's payments always add back up to the bill after tax, tip and any discount.