The formula
Supplier net = Invoice × (1 − w); Gross-up payment = Invoice ÷ (1 − w), w = WHT rate
The gross-up divides rather than multiplies because the tax applies to the grossed amount too: to net the supplier $20,000 under a 10% WHT, the payment must be $22,222 — of which 10% ($2,222) is withheld, leaving exactly $20,000. The buyer’s extra cost is w/(1−w), always more than the headline rate.
The withheld amount is not lost — it is remitted to the tax authority with the supplier’s name attached, and with proper certificates the supplier often credits it against home-country tax under a treaty. The economics of who should bear WHT therefore depend on who can use the credit: a supplier who recovers it fully loses nothing on net treatment.
How to use this calculator
- 1
Determine whether WHT applies
By payment type (services, royalties, interest, fees) and payer country. Domestic rules set the default rate; goods purchases are generally outside scope.
- 2
Check the treaty rate
Double-tax treaties between the two countries frequently reduce the domestic rate — claiming the treaty rate usually needs a tax-residency certificate from the supplier.
- 3
Settle bearing in the contract
Net or gross-up, in writing, before invoicing. This calculator gives both parties the same number to negotiate around.
- 4
Withhold, remit and certificate
The payer deducts, remits to the authority on schedule, and provides the withholding certificate the supplier needs for their foreign tax credit.
The compliance burden sits with the payer
WHT inverts normal tax logic: the payer, not the earner, carries the compliance duty. Failing to withhold does not shift the tax to the supplier — the payer typically remains liable for the amount that should have been withheld, plus penalties and interest. This makes WHT determination a payables-process control, not a supplier problem: every cross-border service invoice should pass a does-WHT-apply check before payment is initiated.
The classification question decides most cases: goods versus services, and within services, which category — technical fees, management fees, royalties and general services often carry different rates. Mixed invoices (equipment plus installation) may need splitting. Where classification is genuinely unclear, a clearing determination from a tax adviser costs less than a withholding failure discovered at audit.
Treaties, certificates and the credit loop
Double-tax treaties exist to prevent the same income being fully taxed twice, and WHT is their main battleground: treaties commonly cap service and royalty withholding below domestic rates, sometimes at zero. Claiming the cap requires paperwork discipline — typically the supplier’s tax-residency certificate obtained before payment — and the payer applying the treaty rate at source rather than the supplier reclaiming later, which can take years where it works at all.
The loop closes with the withholding certificate: proof the tax was withheld and remitted, which the supplier uses to claim a foreign tax credit at home. A supplier who receives certificates promptly and credits fully is economically indifferent to net treatment — which is the fact that unlocks most WHT negotiations. Buyers who run a clean certificate process pay less gross-up, permanently.
Common use cases
Contract negotiation
Put the net and gross-up numbers on the table before signing a services agreement.
Payables compliance
Price the withholding on each cross-border service invoice before initiating payment.
Supplier quote normalisation
Compare a WHT-exposed foreign quote against a domestic one on net-of-everything terms.
Treaty rate checks
Quantify what obtaining a residency certificate saves versus paying the domestic rate.
Automate this with the API
Deliver the computed net or grossed amount with a committed quote.
curl "https://keybs.io/api/v1/tools/quote/live?from=USD&to=KES&amount=20000" \ -H "x-api-key: YOUR_FREE_KEY"Free Tools API docs and key registration
Frequently asked questions
Why does a 10% gross-up cost 11.1%?
Because the withholding applies to the grossed payment as well. Netting the supplier $20,000 under 10% WHT requires paying $22,222 — the tax takes 10% of the larger figure. The general formula is w/(1−w): a 15% WHT costs 17.6% to gross up; 20% costs 25%. The convexity is why gross-up clauses deserve negotiation.
Does WHT apply to goods purchases?
Generally no — WHT regimes target services, royalties, interest, dividends and fees, while goods imports are taxed through customs duty and import VAT instead. Mixed contracts (equipment with installation or training) can trigger WHT on the service element, which is why invoices for mixed supplies are often split.
The supplier says they will just invoice more to cover it — is that a gross-up?
Economically yes, and the calculator’s gross-up figure is what "more" must be — the naive answer of adding 10% to a 10% WHT leaves the supplier short. Contractually, an explicit gross-up clause is cleaner than padded pricing: it adjusts automatically if rates or treaties change, and both sides can see the tax as a tax.
Can the supplier recover what was withheld?
Often, through a foreign tax credit against home-country tax on the same income — if they receive the withholding certificate and their home system grants credits for that country’s WHT. Recovery quality varies from full to nil, and that variance should set the negotiation: full recovery argues for net treatment; nil argues the buyer’s gross-up is a real cost to price into the relationship.
What happens if we simply fail to withhold?
The liability generally stays with the payer: tax authorities assess the unwithheld amount against you, with penalties and interest, regardless of having paid the supplier in full. Cross-border service payments should carry a WHT check in the payables workflow the same way sanctions screening does — before initiation, every time.
Does the payment amount on a KeyBS Pay quote reflect WHT?
The quote commits the FX rate, fee (from 1.5%, route-dependent) and receive amount for the instructed payment — the WHT determination and deduction happen in your payables process before you instruct the net or grossed amount. Run this calculator first, instruct the correct figure, and the quote fixes the delivery of exactly that amount.
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