Working backwards from the amount you want to keep
Most calculators start with gross and subtract. This one starts with the net figure you need — the invoice amount after a client's withholding, the pay after a flat deduction, the price before a percentage is taken off — and finds the gross that produces it. The trap is that you cannot simply add the percentage back on.
The formula
Worked example: $4,000 net after a 20% deduction
- Gross: 4,000 / 0.80 = $5,000
- Deducted: $1,000 — 20% of the gross, 25% of the net
Adding 20% to $4,000 gives $4,800, and 20% off $4,800 is $3,840 — $160 short. Because the deduction is taken from the larger figure, grossing up always needs more than the same percentage added.
The gap grows with the rate
| Net wanted | Deduction rate | Gross needed | "Add the % back" gives | Shortfall |
|---|---|---|---|---|
| $4,000 | 10% | $4,444 | $4,400 | $44 |
| $4,000 | 20% | $5,000 | $4,800 | $200 |
| $4,000 | 30% | $5,714 | $5,200 | $514 |
| $4,000 | 40% | $6,667 | $5,600 | $1,067 |
At 10% the mistake costs $44; at 40% it costs over $1,000. Contractors who quote a net day rate and let the client "add the tax" are systematically underpaid by exactly this amount.
Where grossing up appears
Relocation packages and bonuses that an employer promises "net of tax"; withholding tax on cross-border invoices, where the client deducts 15% or 20% at source; net-pay agreements for domestic staff; and any price quoted after a commission. In each case the party paying needs the gross, and the calculator gives it.
Real tax is not one flat rate
Grossing up a salary for income tax cannot use a single percentage, because the marginal rate changes with the amount. A $4,000 net monthly salary in the US needs roughly $5,100 gross once federal tax and FICA are layered, not the $5,000 a flat 20% suggests. For salaries, use the gross-to-net calculator in reverse; this tool is exact only for a single flat deduction.
What this calculator leaves out
Progressive tax rates, several deductions stacked at different bases, and rounding rules some payroll systems apply.
Related calculators
- Gross to net calculator — the forward direction with real tax bands
- Markup calculator — the same arithmetic on a cost price
- Hourly to salary — quoting a rate that lands where you need it