How SpotCheck works
SpotCheck answers one question with history: for an amount you need by a date, how did different ways of converting it work out in every comparable past period?
The question
Exchange students usually know two things: how much foreign currency they need, and when. What they don't know is whether to convert it all now, spread it out, wait, or hold out for a better rate.
Nobody knows which way exchange rates move next. What can be known is how each of those approaches would have worked out, had the same plan started on any day since 4 Jan 1999. SpotCheck replays your plan over every one of those periods and shows the range of costs, rescaled to today's rate. The result is a record of what happened, not a forecast.
The four strategies
All at once
What you'd do. Convert the whole amount on your start date.
What it trades. You know the exact cost on day one, so there is no range of outcomes. You also give up any chance of a better rate later.
More detailLess detail
In the replay this is the rate on the start date plus your spread. Because every period is rescaled to today's rate, it costs the same in every period, which is why it appears as a single point.
Equal tranches
What you'd do. Convert equal parts on evenly spaced dates from your start date to your deadline.
What it trades. Each part gets a different rate, so the ups and downs partly cancel out. The final cost isn't known until the last part, but no single day decides it.
More detailLess detail
The number of parts is "Most conversions you'd make" under More options. The first part converts on the start date and the last on the deadline. A date with no published rate uses the next available one.
Wait until deadline
What you'd do. Convert everything on the day you need it.
What it trades. The whole cost rides on one day's rate. If the rate moves your way you pay less; if it moves against you, nothing has been converted yet.
More detailLess detail
If the deadline falls on a day with no published rate, the replay uses the next available rate.
Target rate
What you'd do. Pick a rate a little better than today's (2% by default). Convert everything the first day the rate reaches it; if it never does, convert on the deadline.
What it trades. When the target is reached you pay less than today's rate. When it isn't, you end up converting on the deadline, exactly like waiting.
More detailLess detail
The target is set relative to each period's own starting rate, so periods from different years compare fairly. The check on each day only uses rates up to that day, never later ones. You can change the target under More options.
The method
How the replay works
Your plan has a length: the days from your start date to your deadline. SpotCheck takes every day in the rate history since 1999 as a possible start, runs each strategy over the same number of days from there, and records what it would have cost.
A conversion scheduled on a day with no published rate uses the next available rate. Decisions (like whether the target was reached) only ever look at rates up to that day, never later ones.
Why the costs are rescaled to today's rate
A window starting in 1999 at 1.70 SGD per USD isn't comparable with one starting today at around 1.30. So each window's cost is divided by the rate on its own start date, then multiplied by your amount and today's rate. Every outcome then reads: “if the coming months move the way that window did, this is what you'd pay”. That's also why converting everything at once has no range: you know today's rate.
Long trends in the history
The history includes long trends, such as the Singapore dollar strengthening against the US dollar for much of 2004–2013. Any strategy that converts later benefits from a trend like that in the replay. A trend in the past says nothing about the direction of the next few months.
Overlapping windows
Windows that start a day apart share almost all their days, so thousands of windows contain far fewer truly separate histories. The percentages describe this one history; they are not probabilities of what comes next.
The data
Each currency uses one source for its whole history, so there are no jumps where sources switch. For the 27 currencies the European Central Bank has published every working day since 1999 or January 2000 (including USD, EUR, GBP, JPY, AUD, CNY and INR), SpotCheck uses the ECB euro reference rates and derives each SGD rate as (SGD per EUR) ÷ (currency per EUR), both fixed at the same moment each day. The other 12 use Frankfurter's blended central-bank rates, which average sources that fix at different times of day; that smooths daily moves, so daily volatility from them is understated.
Only Monday–Friday trading observations are used. These are mid-market reference rates: banks, cards and money changers charge more, and the spread input adds that cost to every conversion.
- ECB reference rates (27)
- USD, CAD, MXN, BRL, CNY, HKD, JPY, KRW, INR, IDR, MYR, PHP, THB, ILS, TRY, ZAR, AUD, NZD, EUR, CZK, DKK, HUF, NOK, PLN, SEK, CHF, GBP
- Frankfurter blended (12)
- ARS, CLP, COP, PEN, MOP, TWD, VND, KZT, SAR, MAD, ISK, RUB
- Fixed peg (1)
- BND, pegged 1:1 to the Singapore dollar
- Interest rates
- SORA from the Monetary Authority of Singapore and the US federal funds rate from FRED, used only on the Hedging page.
Rates run from 4 Jan 1999 to 30 Oct 2026. An automated job adds each working day's rates, checks them and rebuilds the site.
What it can't tell you
Historical results reflect exchange-rate trends during the periods tested. Different market conditions may produce different outcomes.
How the strategies compare depends on three things: the currency pair, the direction its rate was moving during the periods tested, and the length of the window. A strategy that cost less across one currency's history may have cost more across another's, because their trends differed. The US dollar's history says nothing about the yen's or the euro's; each currency is replayed against its own rates only. Changing the currency, the dates or the number of conversions in the planner shows how much the comparison moves.
It doesn't predict rates or tell you what to do. It shows how simple approaches would have worked out in the past, so you can see the trade-off between a lower average and a narrower range of outcomes.
The rates are mid-market reference rates. Banks, cards and money changers charge more; the spread setting adds that cost to every conversion, but your provider's fees may differ from it.
The Hedging page prices forwards and options from past overnight interest rates and past volatility, a stand-in for the quotes a bank would give. A real quote differs. The Hedging page covers USD only for now.
About SpotCheck
SpotCheck is a free, independent educational project for students going on exchange. It has no accounts, sets no cookies and stores nothing about you: your scenario lives only in the page's address, which is how a copied link reproduces it.
Educational tool using historical mid-market rates. Not financial advice. Past rates don't predict future ones.