Everyday Money Math: Loans, Savings, Tips and Prices

Most everyday money questions come down to a handful of formulas: a loan payment, compound growth, a percentage on or off a price, and a price divided by a size. Free browser calculators run these for you in seconds, and once you have seen one worked example of each, you can judge whether a deal or a number makes sense. This guide walks through real figures for loans, mortgages, savings, bills, sales, VAT, pay, groceries, body measurements and the kitchen.

One note before the numbers. These calculators do arithmetic, not advice. They don't know your taxes, fees, credit history or health, so treat every result as an estimate and check big decisions with a qualified professional, such as a lender, financial adviser or doctor.

How much does a shorter loan really save?

Say you're borrowing 20,000 for a car at 7% a year. Put those figures into the loan payment calculator and try two terms:

Term	Monthly payment	Total interest
5 years	396.02	3,761.44
4 years	478.92	2,988.39

The shorter loan costs 82.90 more each month but 773.05 less in interest overall. The tool uses the standard formula: payment = P × r ÷ (1 − (1 + r)^−n), with r as the monthly rate (annual rate ÷ 12) and n as the number of monthly payments. The yearly amortization table shows how early payments go mostly to interest. It covers principal and interest only, so add any fees yourself.

What does a mortgage cost each month, all in?

A home loan has more moving parts. The mortgage payment calculator adds property tax, home insurance, PMI and HOA fees to the principal and interest. Here is an example with a 350,000 home, 10% down, a 6.5% rate over 30 years, and the default estimates of 1.1% property tax, 1,500 a year for insurance and 0.5% PMI:

• Loan amount: 315,000
• Principal and interest: 1,991.01
• Property tax: 320.83 a month; insurance: 125.00 a month
• PMI: 131.25 a month for 95 months, until the balance reaches 80% of the price
• Monthly payment: 2,568.10, and 401,765.14 in total interest over the full term

Now add 200 a month in extra principal. The loan ends 80 months sooner, PMI drops off after 62 months instead of 95, and you save 104,949.75 in interest. The tax and insurance figures are only placeholders, so replace them with your county's rate and a real quote.

How fast will savings grow?

Compound interest is interest earned on earlier interest, and it rewards time more than anything else. In the compound interest calculator, start with 5,000, add 150 a month, and use 4.5% a year compounded monthly for 10 years:

• Total contributions: 23,000
• Interest earned: 7,514.67
• Final balance: 30,514.67

The year-by-year table shows the interest growing faster each year, from 267.29 in year one to more than 1,200 in year ten. For a quick mental check, the rule of 72 says money doubles in about 72 ÷ 4.5 = 16 years at that rate. The calculator ignores inflation and taxes, so for a rough "real" figure, subtract expected inflation from the rate.

How do you split a bill and get a sale price right?

At dinner, the tip and bill-split calculator does the awkward part. For an 86.40 bill with an 18% tip split three ways, the tip is 15.55, the total is 101.95, and each person pays 33.98. Three times 33.98 is a cent short of the total, so one person rounds up. Whether you tip on the pre-tax or after-tax amount is up to you and local custom.

In a sale, the trap is stacked discounts. The discount calculator takes an original price, a discount and an optional extra discount. A jacket at 80 with 25% off and "an extra 10% at checkout" ends up at 54.00. You save 26, which is an effective discount of 32.5%, not 35%, because the second discount applies to the already reduced price.

How do you add or remove VAT?

Removing tax is where people slip. If a receipt shows 48.00 including 20% VAT, the VAT calculator in Remove VAT from a gross amount mode gives 40.00 net and 8.00 VAT. It divides 48 by 1.20; it doesn't take 20% off 48, which would give 38.40 and be wrong. Switch to Add VAT to a net amount when you're pricing your own work and need the gross figure for an invoice.

What is a salary worth per hour?

To compare a salaried offer with hourly or freelance work, use the salary to hourly calculator. At 52,000 a year, 40 hours a week and 52 paid weeks, the rate is 25.00 an hour, 1,000 a week, and 2,000 every two weeks.

Now drop the paid weeks to 46, as a contractor taking six unpaid weeks off would. The same 52,000 needs 28.26 an hour. That gap is why freelance rates often look high next to salaries. All figures are gross, before tax and deductions.

Is the big pack actually cheaper?

Shelf labels don't always use the same unit, which makes them easy to misread. The unit price calculator compares up to four products, converting each to a common base first. Three bags of coffee:

Product	Price	Size	Per 100 g
Bag A	2.79	400 g	0.6975
Bag B	5.49	1 kg	0.549 (best value)
Bag C	4.29	16 oz	0.9458

Bag A costs 27% more per gram than Bag B, and the 16 oz bag costs 72.3% more. Comparing the cheapest with the most expensive saves 42%. The bulk bag doesn't always win, though, because promotions on small packs can beat it. You can compare weights with weights, volumes with volumes, or item counts, but not weight against volume.

What do BMI and calorie numbers actually tell you?

These two are the easiest to over-read. The BMI calculator divides weight in kilograms by height in meters squared. At 82 kg and 178 cm that's 25.9, which falls in the WHO "overweight" band for adults, and the healthy-weight range for that height is shown as 58.6–78.9 kg. BMI can't tell muscle from fat, and it says nothing about where weight is carried, so a muscular person can score "overweight" while being perfectly healthy. Use it as a rough screening number, not a verdict.

The daily calorie calculator uses the Mifflin-St Jeor equation. For a 32-year-old woman at 70 kg and 170 cm, the basal rate is 1,442 kcal a day. With light activity (1–3 days of exercise a week), maintenance is about 1,982 kcal. The "lose 0.5 kg per week" goal subtracts 550 kcal, giving a 1,432 kcal target, with a balanced split of 107 g protein, 143 g carbohydrate and 48 g fat. Targets are never set below 1,200 kcal for women or 1,500 kcal for men. Real metabolism varies, so if you have a health condition, talk to a doctor or dietitian before following any target.

Can the same approach help in the kitchen and on the road?

Yes. Both just need the right conversion. In the cooking measurement converter, pick the ingredient before converting cups to grams. 1½ US cups of granulated sugar is about 297 g, but the same cups of all-purpose flour is only about 180 g, and a US stick of butter is about 113 g. The weights assume a spooned and levelled cup, so a kitchen scale is still more accurate.

For driving costs, the fuel economy converter handles the reciprocal math between distance-per-fuel and fuel-per-distance. A car rated at 6.5 L/100 km does about 36.2 US mpg, or 43.5 UK mpg, because the imperial gallon is bigger. A 600 km trip at that rate needs about 39 liters, so multiply by your local fuel price to budget it.

All of these calculators work in your browser as you type, and you don't need to sign up.

FAQ

Are these calculators financial or medical advice?

No. They do the standard math on the numbers you enter. They don't know your taxes, fees, credit terms or health, so check important decisions with a qualified professional.

Why doesn't my bank's loan payment match exactly?

Lenders may add fees, round differently, or calculate interest daily. The loan calculator covers principal and interest only, so small differences are normal.

Which currency do the calculators use?

Any currency. Amounts are plain numbers, so enter prices in whatever currency you use.

Is BMI accurate for everyone?

No. It's a quick population-level screen. It can misclassify athletes, older adults and people of different body types.

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