A budget exchange rate is the rate fixed when a budget is set, at which cloud cost priced in another currency is converted for the comparison with the budget. A company that plans in euros or pounds while the providers price in US dollars needs one, because the invoice is produced at a rate the provider chooses and dates. Without a fixed rate, the budget variance mixes consumption with currency, and a team ends up explaining an overrun it did not cause.
How it works
Three rates meet. The budget rate is approved with the budget and holds for the whole budget period. The provider's rate is in the invoice and in the billing data; how each provider chooses it is described in invoice currency and exchange rates. And accounting books the invoice at the rate its accounting policy prescribes.
For the budget, the currency the tools calculate in also matters. Azure evaluates a budget on a billing profile or invoice section in the billing currency, but one on the billing account of a Microsoft Customer Agreement in US dollars (cloud budgets). A Google budget's Pub/Sub message states in currencyCode the currency of its costs and amounts. AWS Cost Explorer shows costs only in US dollars.
The options
Which kind of rate the budget rate is, finance or treasury decides, and the cloud budget takes it from the rest of the company plan. No option is right or wrong; they measure different things.
| Option | Set as | What it reflects | What to watch |
|---|---|---|---|
| Spot rate on the budget date | the rate on the day the budget is set | the market at the time of the decision | depends on a single day |
| Average rate | the mean over a past period | the market without daily swings | lags the market |
| Forward or hedged rate | the rate treasury has secured or assumes | what the company pays for hedged amounts | covers only the hedged part |
| Rate set by controlling | one rate for every plan in the company | consistency with the rest of the plan | comes from one of the rows above |
One documented source for a spot rate or an average is the European Central Bank's euro reference rates, US dollar and pound sterling among them; the ECB Data Portal also holds them as monthly series of averages, such as EXR.M.USD.EUR.SP00.A. For sterling, the Bank of England publishes daily spot rates against the pound and states that they are not official rates. The ECB quotes every currency against the euro, so dollars per euro; the calculation below needs euros per dollar, which is the reciprocal.
The calculation
With c as cost in the pricing currency, kB as the budget rate and kA as the provider's rate, both expressed as budget currency per unit of pricing currency:
Budget B = Σ cB · kB
Actual at the budget rate AB = Σ cA · kB
Actual at the provider rate AA = Σ cA · kA
Usage and price effect AB − B
Currency effect AA − AB = Σ cA · (kA − kB)
Total variance AA − B
The billing data supplies the cost in the pricing currency, per provider in the fields invoice currency and exchange rates names, in FOCUS in PricingCurrencyEffectiveCost. How the usage and price effect splits further into volume, price and mix is shown in variance analysis for cloud cost.
At reforecast
The budget rate stays fixed for the approved budget even when the market moves; only then do the months' variances stay comparable. The forecast, by contrast, may use a current rate, so that finance sees where the invoice will land. If the budget is approved again at a reforecast, it gets a new budget rate with a date and a source, and variances before and after the change are reported separately.
What it means for your cost
The budget rate changes no invoice. It assigns who explains a variance: the usage and price effect belongs to the teams and to whoever owns commitments; the currency effect belongs to finance or treasury, and no team removes it by switching something off. Team budgets are therefore measured at the budget rate, the total budget for cash planning also at the provider's rate, and both figures stand side by side. In the monthly cloud cost review the currency effect is a line of its own.
Two things follow for the budgets in the providers' tools. A budget evaluated in the billing currency uses the provider's rate and so also reports currency moves. A budget evaluated in dollars, as on Azure at the billing account of a Microsoft Customer Agreement, needs as its amount the euro or sterling budget divided by the budget rate. How the annual budget fixes the rate together with the amount is covered in building the annual cloud budget.
Four facts are recorded: the rate, the direction of the quotation, the source and the date. At which rate accounting books an invoice and how it treats exchange differences is set by the company's accounting policy and its auditor; the budget rate is a steering figure, not a booking rule.
Where it goes wrong
- No budget rate. Symptom: the euro budget is exceeded while dollar cost is unchanged. Cause: actuals were converted at the provider's rate and the budget at no fixed rate, so the currency effect appears as extra consumption.
- The rate upside down. Symptom: converted amounts are clearly off. Cause: the ECB quotes dollars per euro, and converting dollar cost into euros needs the reciprocal.
- The budget rate replaced without a date. Symptom: the currency effect vanishes from one month to the next although the rate has not moved. Cause: the budget rate was quietly replaced by a current one, and the months before and after no longer compare.
- Invoice reconciliation at the budget rate. Symptom: actuals at the budget rate do not match the invoice. Cause: the invoice is produced at the provider's rate; the budget rate is for steering, not for reconciliation.
- A dollar budget on Azure overlooked. Symptom: an Azure budget on the billing account alerts at different points from the euro plan. Cause: it is evaluated in US dollars there, regardless of the billing currency.
Sources
Read on 2026-10-16. European Central Bank Euro foreign exchange reference rates and US dollar per euro monthly series in the ECB Data Portal; Bank of England Daily spot exchange rates against sterling; AWS Exploring your data using Cost Explorer; Microsoft Create and manage budgets; Google Cloud Set up programmatic notifications; FOCUS 1.4 Pricing Currency Effective Cost.