Solverly

Sales Tax Calculator

See the real cost at checkout before you swipe. The Sales Tax Calculator shows how a listed price turns into a final total once local tax is applied, and it’s just as useful for backing into the pre-tax amount from a receipt. Use it when budgeting a purchase, comparing in-store vs. online offers, or checking whether a quoted price already includes tax.

This tool lets you forecast totals for carts of any size, reverse-engineer tax from a paid amount, and sanity-check invoices so there are no surprises at the register. The goal is simple: turn price tags into clear, predictable out-the-door numbers—so you can plan spending, split costs fairly with friends or coworkers, and make quick, confident decisions while shopping or preparing reimbursements.

Enter a subtotal or total to calculate sales tax, tip, and the final bill with step-by-step breakdowns and worked examples.

Enter amounts

Quick breakdown

Mode
From subtotal
Decimals
2
Subtotal
$100.00
Tax amount
$8.25
Tip amount
$0.00
Total
$108.25

Step-by-step math

From subtotal: tax = subtotal × taxRate, tip = subtotal × tipRate, total = subtotal + tax + tip.

From total (reverse): subtotal = total ÷ (1 + taxRate + tipRate), then compute tax and tip from that subtotal.

Results interpretation

We round to the decimals you choose. Two decimals match most receipts. When rates are high or totals large, a one-cent difference can appear from rounding; that’s normal across registers.

  • From subtotal: the tax amount tells us what portion goes to tax; the total is what we pay.
  • From total: the reverse breakdown shows the implied pre-tax price and tax share.
  • Tip: we treat tip as a percent of the subtotal, which matches typical dining receipts.

How it works

We apply a simple linear model that works across any percentage. Tip is optional and applied to the subtotal.

Formulas, assumptions, limitations

Formulas: total = subtotal × (1 + tax + tip); subtotal = total ÷ (1 + tax + tip).

Assumptions: tip is based on subtotal; tax applies to pre-tip subtotal; no extra fees.

Limitations: some locales tax certain fees or apply tiered rates; adjust the subtotal or rates to match your case.

Use cases & examples

Retail purchase

Subtotal $58.00, tax 8% → tax $4.64, total $62.64.

Restaurant bill

Subtotal $86.50, tax 8.25%, tip 18% → total ≈ $111.72.

Reverse from total

Total $108.25, tax 8.25%, tip 0% → subtotal ≈ $100.00, tax ≈ $8.25.

Sales tax FAQs

How do we compute tax from subtotal?

Multiply subtotal by the tax rate. Add it to the subtotal for the total.

How do we get the subtotal from a total?

Divide the total by (1 + taxRate + tipRate). Then compute the tax from that subtotal.

Is tip taxed?

In many places, tip is not taxed when it’s voluntary. We calculate tip from subtotal and tax from subtotal.

What if there’s a service fee?

Add it to the subtotal first or incorporate it into an effective rate before computing.

Which rounding should we use?

Two decimals match standard currency display; choose more if you need exact fraction math.

Can we use decimal tax rates like 8.875%?

Yes. Enter any percentage; results update instantly.

Why does reverse math differ by a cent?

Rounding during each step can shift the final cent. Registers handle this the same way.

Can we export a link with our inputs?

Use the copy link button under the inputs; it preserves mode, amounts, rates, and decimals.

Sales Tax Math: Practical Guide for Everyday Decisions

We built our calculator to make short work of retail, dining, and service receipts. Small percentage differences add up, so we surface the moving parts—subtotal, tax, tip, and total—and let you toggle between forward and reverse math without friction.

Why a simple percentage model works so well

Most everyday purchases follow a straightforward rule: compute a percentage of the pre-tax price for tax, and optionally compute a percentage of that same price for tip. Because the relationships are linear, you can move in either direction with a single multiplier. That’s why forward math (adding tax and tip) and reverse math (backing out tax and tip) are both stable and easy to verify.

Forward math: from subtotal to total

When we start with a subtotal, we multiply by the tax percentage to get the tax amount. If a tip applies, we multiply the subtotal by the tip percentage. Add those pieces to the subtotal to get the total. As a quick mental check, multiply the subtotal by (1 + tax + tip); the result should be within a cent of the detailed sum when using two decimals.

Reverse math: from total back to subtotal

Reverse math is the same idea inverted: divide the total by (1 + tax + tip). That yields the implied pre-tax subtotal. Multiply that number by the tax percentage to recover the tax amount, and by the tip percentage to recover the tip. This is useful when we only remember the final amount or when we want to compare pre-tax prices across stores or tipping options.

Rounding choices and why a penny moves

Businesses typically round currency to two decimals. If we round after each step (tax and tip) instead of at the very end, the final cent can land differently. Our calculator lets you choose decimals so you can match a receipt’s behavior or keep more precision for analysis. Either way, the differences stay inside a one-cent band on typical receipts.

Edge cases we see in the wild

Some places compute tip on top of tax, or tax certain fees. Others apply multiple stacked rates (state + county + city). In those cases, convert the details into an effective rate or add the fee to the subtotal first. If you’re auditing a receipt, try matching the business’s step order: compute the same pieces, round the same way, then compare.

Sanity checks you can do in seconds

A quick check is to estimate the tax as 10% when the rate is near that number. If the actual rate is 8.25%, mentally shave a bit off your 10% estimate. For a $100 subtotal, that means $8.25, so a total around $108.25 (before tip). These checks are fast and keep surprises off your bill.

Planning purchases with totals in mind

When a budget target is fixed—say we want to spend exactly $150—reverse mode tells us how much merchandise we can buy after tax (and tip). Divide by (1 + tax + tip) and aim for a subtotal at or below that number. This is especially handy for group orders or gift cards with hard caps.

Receipts, reimbursements, and policies

Some workplaces reimburse pre-tax amounts only, others reimburse tax but not tip, and a few reimburse the entire total. Our breakdown clarifies what portion is merchandise, what portion is tax, and which part is the gratuity. That makes filling forms and expense reports faster and more consistent.

Tips for consistent results

  • Use exact posted rates (e.g., 8.875%) for accurate results.
  • Match decimals to your receipt format when reconciling cents.
  • If fees are taxed, add them to the subtotal before calculating tax.
  • When comparing stores, compare either pre-tax or post-tax amounts consistently.

Bringing it all together

Sales tax math doesn’t need to be slow. With a clear model and a couple of simple formulas, we can move forward or backward, explain every cent on a receipt, and make smarter choices with the numbers in front of us.