Add or reverse sales tax, and separate profit margin from markup with a single tool. It is built for both shoppers who want the pre-tax price behind a register total and small business owners who need to price products to hit a real margin target.

Mortgage Calculator

Calculate monthly payments, total interest, and loan breakdown.

Auto-fill Tax & Insurance by Zip Code

Home Price

$

Down Payment

%

Interest Rate

%

Loan Term

yrs

Extra Monthly Principal

$

Annual Property Tax

$

Annual Home Insurance

$

One-Time Lump Sum

$

Down Payment$70,000.00

Loan Amount$280,000.00

Total Interest$357,124.57

Total Paid$637,124.57

P&I Payment$1,769.79

Payment Breakdown

Annual Payment Split

Remaining Loan Balance Over Time

Cumulative Interest Paid vs. Principal Recovered

Early in the loan, most payments go to interest — see when the balance shifts

💡 Principal recovered exceeds cumulative interest at Year 0 — before this point, most of your payments fund interest.

Add or reverse sales tax, and separate profit margin from markup with a single tool. It is built for both shoppers who want the pre-tax price behind a register total and small business owners who need to price products to hit a real margin target.

Loan Term Comparison

15 vs 20 vs 30-year breakdown at 6.5% · $280,000 loan

Term	Monthly Payment	Total Interest	Total Paid	vs 30yr Interest
15-year	$2,439.10	$159,038	$439,038	−$198,086
20-year	$2,087.60	$221,025	$501,025	−$136,099
30-year	$1,769.79	$357,125	$637,125	baseline

15-Year Term

Monthly Payment$2,439.10

Total Interest$159,038

Total Paid$439,038

Interest Saved vs 30yr−$198,086

20-Year Term

Monthly Payment$2,087.60

Total Interest$221,025

Total Paid$501,025

Interest Saved vs 30yr−$136,099

30-Year Term

Monthly Payment$1,769.79

Total Interest$357,125

Total Paid$637,125

How This Calculator Works

A mortgage is an amortizing loan used to buy a home, repaid in fixed monthly installments across a set term (commonly 15 or 30 years). Each payment splits into two parts: principal, the borrowed amount you are paying back, and interest, the lender's fee calculated on the remaining balance. Because interest is charged on the outstanding balance, early payments are interest-heavy — a pattern called front-loaded amortization. Your down payment reduces the loan size; a 20% down payment also avoids Private Mortgage Insurance (PMI). Adding extra principal each month reduces the balance faster, which shrinks future interest and shortens the term. The PITI figure combines principal and interest with property tax and homeowners insurance to show your true monthly housing cost, which is what lenders use when qualifying you against a debt-to-income ratio.

The Mathematical Formula & Logic

The standard amortization formula for the fixed monthly principal-and-interest payment is M = P × [ r(1 + r)ⁿ ] / [ (1 + r)ⁿ − 1 ]. P is the loan principal (home price minus down payment). r is the monthly interest rate (annual rate ÷ 12, expressed as a decimal). n is the total number of monthly payments (loan term in years × 12). Total interest paid over the loan equals (M × n) − P. Each month the remaining balance updates as B_new = B_old × (1 + r) − M.

Worked Step-by-Step Example

Consider a $350,000 home with a 20% down payment on a 30-year fixed loan at 6.5% interest. The down payment is $70,000, so the loan principal P = $280,000. The monthly rate r = 0.065 ÷ 12 = 0.0054167, and n = 360 payments. Plugging into the formula gives a monthly P&I payment of about $1,771.66. Over 360 months you pay $637,798 total, of which $357,798 is interest. Adding a $200/month extra principal payment reduces total interest by roughly $97,000 and pays the loan off about 6 years early.

Frequently Asked Questions

P&I is just principal and interest. PITI adds property taxes and homeowners insurance to show your full monthly housing cost. Lenders qualify you on PITI when measuring debt-to-income, not on P&I alone.

Every extra dollar above your scheduled payment reduces principal directly. Because interest is charged on the remaining balance, a lower principal means less interest accrues each month — a compounding saving that also shortens the loan term.

PMI is required below a 20% down payment. By law it is automatically canceled at 78% loan-to-value, and you can request removal at 80% LTV with a good payment history. Extra principal payments help you reach that threshold sooner.

Refinancing pays off when the interest savings offset closing costs (typically 2–5% of the loan). A common rule is to refinance when rates drop at least 1% below your current rate and you will stay in the home past the break-even point shown in the Refinance tab.

Disclaimer: CompelKit tools and calculators are provided for educational and estimation purposes only and do not constitute certified legal, financial, or tax advice.

Read the full guide: How Mortgage Amortization Really Works →

Audio Editor

Trim, adjust and export using the menu bar above

Drop an audio file here

or click to browse — MP3, WAV, OGG, FLAC, AAC, M4A

Tip: use File menu or drag a file to get started

How to use the Audio Editor

Load audio via the drop zone above, File → Open, Load from URL, or record directly from your microphone.
Drag the Trim Start / Trim End sliders to select the section you want to keep.
Adjust Volume, or open the Effects menu for gain, fades, EQ, noise reduction, and more.
Use Edit → Undo/Redo at any point to step back through your changes.
Export your result from the Quick Export buttons or File → Export as MP3, WAV, OGG, AAC, or FLAC.

Everything runs locally in your browser — no files are uploaded to a server.

How This Calculator Works

The CompelKit audio editor runs entirely in your browser using ffmpeg.wasm, so your files are never uploaded to a server. You can load an audio file, trim it to a region, apply effects (fade, normalize, speed, volume, EQ), and export to MP3, WAV, OGG, AAC, or FLAC. Editing is non-destructive: trims and effect settings are stored as parameters and applied during export, so you can adjust and re-export without quality loss from repeated re-encoding of the source. Multitrack mixing lets you layer two clips and balance their levels before export.

The Mathematical Formula & Logic

Trim region is encoded as a start time and end time (in seconds).

Export pipeline = ffmpeg filter chain applied to the source: trim → effects (fade, volume, atempo) → encoder (libmp3lame, pcm_s16le, libvorbis, aac, flac). Output file size follows the bitrate formula: (Bitrate × Duration) / 8 / 1024 MB.

Worked Step-by-Step Example

Trim a 3:00 clip to the first 2:30 by setting the end marker to 2 minutes 30 seconds, then export to MP3 at 128 kbps. The exported file is 2:30 long and about (128 × 150) / 8 / 1024 ≈ 2.34 MB — no upload, no server round-trip, the entire operation runs locally in your browser.

Frequently Asked Questions

Yes. All processing uses ffmpeg.wasm compiled to WebAssembly and runs locally in your browser tab. Your audio files are never uploaded to a server, so they stay on your device throughout editing and export.

Import supports MP3, WAV, FLAC, AAC, M4A, OGG, Opus, AIFF, and more. Export to MP3, WAV, OGG, AAC, or FLAC. WAV and FLAC are lossless; MP3, OGG, and AAC are compressed and let you choose a bitrate to balance quality and size.

No. Trims are stored as a region (start and end time) and applied once during export, so the source buffer isn't re-encoded until the final export. Repeated adjustments and re-exports don't compound quality loss the way repeatedly re-saving a lossy file would.

Disclaimer: CompelKit tools and calculators are provided for educational and estimation purposes only and do not constitute certified legal, financial, or tax advice.

Read the full guide: A Browser-Based Audio Editor Explained →

Add or reverse sales tax, and separate profit margin from markup with a single tool. It is built for both shoppers who want the pre-tax price behind a register total and small business owners who need to price products to hit a real margin target.

Currency Converter

Real-time exchange rates powered by Frankfurter (ECB data)

Amount

From

Converted Amount

—

To

Could not load exchange rates. Check your connection and try again.

Select currencies above

How This Calculator Works

Currency conversion multiplies an amount in one currency by the exchange rate to express it in another. Exchange rates fluctuate continuously based on supply and demand in foreign-exchange markets, central bank policy, interest rates, and trade flows. This tool pulls live mid-market rates so the result reflects the current wholesale rate; the rate a consumer actually receives at a bank or kiosk adds a margin (a spread), so the amount you convert at the airport is usually worse than the mid-market figure shown here. Use the comparison view to see several currencies at once and the historical chart to gauge whether a rate is favorable relative to the recent past.

The Mathematical Formula & Logic

Converted Amount = Amount × Rate (units of target currency per one unit of source currency). To invert: Rate_inverse = 1 ÷ Rate. A percentage change over time = ((Rate_now − Rate_then) ÷ Rate_then) × 100.

Worked Step-by-Step Example

Converting $1,000 USD to EUR at a rate of 0.92 euros per dollar gives 1,000 × 0.92 = €920. If the rate a week earlier was 0.90, the dollar strengthened by ((0.92 − 0.90) ÷ 0.90) × 100 ≈ 2.22%, meaning your $1,000 buys about €20 more than it did last week. A bank charging a 3% margin would give you only about €892 instead of the €920 mid-market figure.

Frequently Asked Questions

The mid-market rate is the midpoint between buy and sell prices on global currency markets — the true wholesale rate. Retail providers add a spread on top, so consumers rarely receive exactly this rate.

Rates move with supply and demand, driven by interest rates, inflation, trade balances, central bank policy, and geopolitical events. Higher local interest rates usually strengthen a currency.

No one can time the market reliably, but checking a historical chart helps you see if today's rate is high or low relative to the recent range. For large conversions, avoid airport kiosks with wide spreads.

Providers charge either a fixed fee, a percentage spread, or both. The spread is the difference between the rate you get and the mid-market rate — often the largest hidden cost of converting money.

Disclaimer: CompelKit tools and calculators are provided for educational and estimation purposes only and do not constitute certified legal, financial, or tax advice.

Read the full guide: How Currency Exchange Rates Actually Work →

Add or reverse sales tax, and separate profit margin from markup with a single tool. It is built for both shoppers who want the pre-tax price behind a register total and small business owners who need to price products to hit a real margin target.

Budget Planner

Plan and track your monthly income and expenses.

Monthly Income / Revenue

$

Expense Categories

Category	Budgeted	Actual	Diff
			+$1,500.00
			+$200.00
			+$400.00
			+$300.00
			+$250.00
			+$150.00
			+$200.00
			+$500.00
			+$100.00
			+$100.00

Totals	$3,700.00	$0.00

Total Income$5,000.00

Total Spent$0.00

Remaining Balance$5,000.00

💡 Home Budget Tips

• Follow the 50/30/20 rule (needs/wants/savings)
• Track your spending for the first month
• Build an emergency fund first
• Review subscriptions and cancel unused ones
• Meal plan to reduce grocery costs
• Automate your savings contributions

How This Calculator Works

A budget divides income into planned categories so you can see where money goes and adjust before overspending. This planner supports two templates: a personal (home) budget using the 50/30/20 framework (needs, wants, savings) and a business budget that separates cost of goods, operating expenses, and owner compensation with a tax reserve. Each category is editable, with subtotals for income and expenses and a net surplus or deficit that updates live. The business tab also estimates a quarterly tax reserve so owners set aside funds as they earn rather than scrambling at filing time.

The Mathematical Formula & Logic

Net = Total Income − Total Expenses. For the home budget, target allocation = Income × percentage (50% needs, 30% wants, 20% savings/debt). For the business budget: Net Operating Income = Revenue − COGS − Operating Expenses; Owner Draw = Net Operating Income − Tax Reserve; Tax Reserve = Taxable Income × estimated effective rate ÷ 4 per quarter.

Worked Step-by-Step Example

On $5,000 monthly take-home, the 50/30/20 split allocates $2,500 to needs, $1,500 to wants, and $1,000 to savings or debt payoff. A business with $8,000 monthly revenue, $2,500 COGS, and $3,000 operating expenses has $2,500 in net operating income; setting aside 25% for taxes ($625/month) leaves $1,875 for owner draw and reinvestment — tracked across the full year to avoid a tax surprise.

Frequently Asked Questions

50% of income to needs (housing, food, utilities), 30% to wants, and 20% to savings or debt payoff. It is a flexible starting point, not a strict rule — adjust the splits to fit your goals.

Zero-based budgeting assigns every dollar a job so income minus expenses equals exactly zero. It forces intentional spending and is more precise than defaulting leftover money to 'savings.'

Self-employment income usually has no withholding, so setting aside a percentage each month prevents a cash crunch at filing time. Many owners target 25–30% of profit as a safe reserve.

Review monthly and re-baseline quarterly. A monthly check catches overspending early; a quarterly reset adjusts categories based on what actually happened and changed goals.

Disclaimer: CompelKit tools and calculators are provided for educational and estimation purposes only and do not constitute certified legal, financial, or tax advice.

Read the full guide: Budgeting Frameworks That Actually Work →

Add or reverse sales tax, and separate profit margin from markup with a single tool. It is built for both shoppers who want the pre-tax price behind a register total and small business owners who need to price products to hit a real margin target.

Sales Tax & Margin Calculator

Reverse sales tax and profit margin/markup calculations.

Total Price (incl. tax)

$

Tax Rate

%

Tax Amount$7.62

Pre-Tax Price$92.37

How This Calculator Works

Sales tax is a percentage added to the retail price of taxable goods and services at the point of sale, set by state and local governments in the United States. This calculator handles two related jobs: forward calculation, which adds tax to a pre-tax price to get the total at the register, and reverse calculation, which extracts the original pre-tax price from a final amount that already includes tax. It also computes profit margin and markup, which are frequently confused: margin is profit as a share of the selling price, while markup is profit as a share of the cost. Knowing the difference matters for pricing, because a 25% margin is not the same as a 25% markup.

The Mathematical Formula & Logic

Total = Price × (1 + taxRate). To reverse out the pre-tax price from a tax-inclusive total: Price = Total ÷ (1 + taxRate). Tax collected = Total − Price. Profit margin = (Selling Price − Cost) ÷ Selling Price. Markup = (Selling Price − Cost) ÷ Cost. Rates are entered as decimals (7% = 0.07).

Worked Step-by-Step Example

A $50 item in a jurisdiction with 7% sales tax: Total = $50 × 1.07 = $53.50, and the tax collected is $3.50. Reversing it: if you only know the register total of $53.50, the pre-tax price is $53.50 ÷ 1.07 = $50. For margins: buy for $40, sell for $50 → margin = ($50−$40)/$50 = 20%, while markup = ($50−$40)/$40 = 25% — same dollars, different bases.

Frequently Asked Questions

Forward tax starts from a pre-tax price and adds the tax to reach the register total. Reverse tax starts from a final, tax-inclusive total and backs out the original price and the tax portion using the same rate.

Margin divides profit by the selling price, while markup divides profit by the cost. A 25% margin equals a 33% markup on the same numbers, so mixing them up leads to systematic underpricing.

The seller collects sales tax at the point of sale and remits it to the state tax authority. If you run a business, you are generally responsible for tracking nexus rules and filing returns on schedule.

No. Most states exempt groceries, prescription drugs, and some services, and many have sales-tax holidays. Taxability depends on your state and the product category, so check your local rules for specifics.

Disclaimer: CompelKit tools and calculators are provided for educational and estimation purposes only and do not constitute certified legal, financial, or tax advice.

Add or reverse sales tax, and separate profit margin from markup with a single tool. It is built for both shoppers who want the pre-tax price behind a register total and small business owners who need to price products to hit a real margin target.

Sales Tax & Margin Calculator

Reverse sales tax and profit margin/markup calculations.

Total Price (incl. tax)

$

Tax Rate

%

Tax Amount$7.62

Pre-Tax Price$92.37

How This Calculator Works

Sales tax is a percentage added to the retail price of taxable goods and services at the point of sale, set by state and local governments in the United States. This calculator handles two related jobs: forward calculation, which adds tax to a pre-tax price to get the total at the register, and reverse calculation, which extracts the original pre-tax price from a final amount that already includes tax. It also computes profit margin and markup, which are frequently confused: margin is profit as a share of the selling price, while markup is profit as a share of the cost. Knowing the difference matters for pricing, because a 25% margin is not the same as a 25% markup.

The Mathematical Formula & Logic

Total = Price × (1 + taxRate). To reverse out the pre-tax price from a tax-inclusive total: Price = Total ÷ (1 + taxRate). Tax collected = Total − Price. Profit margin = (Selling Price − Cost) ÷ Selling Price. Markup = (Selling Price − Cost) ÷ Cost. Rates are entered as decimals (7% = 0.07).

Worked Step-by-Step Example

A $50 item in a jurisdiction with 7% sales tax: Total = $50 × 1.07 = $53.50, and the tax collected is $3.50. Reversing it: if you only know the register total of $53.50, the pre-tax price is $53.50 ÷ 1.07 = $50. For margins: buy for $40, sell for $50 → margin = ($50−$40)/$50 = 20%, while markup = ($50−$40)/$40 = 25% — same dollars, different bases.

Frequently Asked Questions

Forward tax starts from a pre-tax price and adds the tax to reach the register total. Reverse tax starts from a final, tax-inclusive total and backs out the original price and the tax portion using the same rate.

Margin divides profit by the selling price, while markup divides profit by the cost. A 25% margin equals a 33% markup on the same numbers, so mixing them up leads to systematic underpricing.

The seller collects sales tax at the point of sale and remits it to the state tax authority. If you run a business, you are generally responsible for tracking nexus rules and filing returns on schedule.

No. Most states exempt groceries, prescription drugs, and some services, and many have sales-tax holidays. Taxability depends on your state and the product category, so check your local rules for specifics.

Disclaimer: CompelKit tools and calculators are provided for educational and estimation purposes only and do not constitute certified legal, financial, or tax advice.

CompelKit