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Why the rate on a transfer is the thing most apps get wrong

You take 500 euros to an exchange office and walk out with dinars. The office took a cut — that is how exchange offices live. Almost every budgeting app will record this conversion at the official mid-market rate, which means the cut you just paid vanishes from your records. You are quietly richer on paper than you are in your pocket.

Where the money goes

An exchange is not an expense: you still have the money, just in a different form. So an app should not record it as spending — that would make a trip to the exchange office look like you lost 500 euros.

But it is not nothing, either. The difference between the official rate and the one you got is a real cost, and over a year of changing money monthly it adds up to a meaningful number. An app that converts at the official rate records neither the expense nor the cost. The money simply reappears on the other side, slightly more of it than you actually received.

Keeping both amounts

The fix is boring and complete: store what left and what arrived, as two facts, and do not compute either one.

If 500 euros left and 58 200 dinars arrived, those are the two numbers. The rate is whatever they imply — 116.4 — and that is the rate you actually got, spread included. Nothing needs to be looked up, nothing needs a rate service, and the record stays true forever because it never depended on a rate in the first place.

Where rates are still used, and where they are not

A rates service is still needed for one job: showing the total across wallets in the one currency you think in. That number is a convenience and it moves with the market, which is correct — it is answering "what is all of this worth today".

Everything you typed in stays exactly as typed. A rate change never rewrites a past transaction, so last March's spending reads in March's terms, and comparing months means something. The app refreshes rates in the background and keeps the last set it downloaded, so the total still works offline.

How to record an exchange

On the Wallets tab, tap − on the wallet the money left.
Enter the amount that actually left — the 500.
Pick the Transfer category instead of a normal expense category.
Choose the wallet the money arrived in. Since its currency differs, the Transfer with conversion screen opens.
Enter the amount that actually arrived — the 58 200 — and save. Both wallets update, the pair is one transaction, and the rate in your history is the one the office gave you.

Questions

Why not just let the app use the official rate and be done?

Because then your records describe a transaction that did not happen. The official rate is a market average; nobody outside a trading desk gets it. Recording it makes your balances slightly wrong in a direction you will never notice and never correct.

Does this mean I have to enter two numbers every time?

Yes, and both are on the receipt in front of you. It is one extra field in exchange for a history that stays true.

Can I see what the exchange actually cost me?

Compare the implied rate with the market one for that day. Walletable does not do that arithmetic for you, which is worth saying plainly — it keeps the honest numbers so the comparison is possible, and that is where it stops today.

What about card payments in a foreign currency?

Those are a normal expense in the wallet's own currency, not a transfer. Your bank already did the conversion and charged you its own rate; the amount that left your account is the fact to record.