WooCommerce Product Add-ons: Why Flat Fees Do Not Convert
TL;DR
- Compatible? Yes. WooCommerce Product Add-ons works with the Aelia Currency Switcher.
- What you need: Currency Switcher 3.2.x or later, Product Add-ons 2.5.3 or later, and the free Product Add-ons Integration add-on.
- Why the add-on matters: flat-fee options do not convert on their own. A £15.00 gift wrap stays “15” in every currency without it.
- Percentage fees convert correctly either way, because they are relative to a price that has already been converted.
WooCommerce Product Add-ons is the extension most stores reach for when a product needs options that change the price: engraving, gift wrap, an extended warranty, a choice of finish. It works well, and on a single-currency store there is nothing to think about.
Add a second currency and one specific thing breaks in a way that is easy to miss: the fixed fees. This review covers what Product Add-ons does, exactly where it falls short on international stores, and the free integration that fixes it.
What WooCommerce Product Add-ons Does
Product Add-ons lets you attach extra option fields to a product, and lets those fields change what the customer pays. Originally built by Mike Jolley, it is now sold through the official WooCommerce marketplace at $59.00 per year for a single site.
It is aimed at stores selling anything configurable or personalised: print shops, furniture, gifting, food hampers, equipment hire. The field types are the part that matters for this review, because they behave differently once a second currency is involved.
The Field Types, and Which Ones Carry a Price
- Flat fee. A fixed amount added to the total. The one that breaks in multi-currency.
- Percentage fee. A proportion of the product price. Converts correctly on its own.
- Custom price. The customer enters an amount. Needs a decision about which currency they are typing in.
- Quantity-based fee. A flat fee multiplied by a number. Inherits the flat-fee problem.
- Image-based selections, dropdowns, checkboxes, text input. Presentation only until you attach a fee to them.
Where Product Add-ons Falls Short on International Stores
Here is the failure in one example. You sell a print at £40.00 and offer framing as a flat-fee add-on at £15.00. A customer in Germany switches to euros. The print converts correctly and shows as roughly 46,00 €. The framing fee shows as 15,00 €.
Not 17,25 €. Fifteen. The number was stored as “15” against the product and nothing told it that the currency had changed, so it is served unchanged with a euro symbol in front of it. You have just discounted your framing by about 13% for every euro customer, silently, on every order.
The mechanism is worth understanding because it explains the pattern. The Currency Switcher converts the product price through WooCommerce’s pricing layer. An add-on fee is separate data attached to the product, and Product Add-ons does not pass it through that layer for conversion. Percentage fees escape the problem entirely, because 10% of an already-converted price is correct in any currency. It is only the fixed amounts that go wrong.
Why This One Is Easy to Miss
Nothing errors. No warning appears, no order fails, and the totals all add up correctly. The only symptom is margin quietly leaving on add-on revenue in every currency except your base one. Most stores find it in a reconciliation months later, which is why it is worth checking before launch rather than after.
What the Add-on Pricing Gap Costs You, in Numbers
Take the framing example and follow it through three configurations. The product is a print at £40.00, the framing add-on is £15.00, and the exchange rate is 1.15 euros to the pound.
| Configuration | Framing add-on | Order total | Margin effect | |
|---|---|---|---|---|
| Base currency, GBP | £40.00 | £15.00 | £55.00 | Correct |
| EUR, no integration add-on | 46,00 € | 15,00 € | 61,00 € | 2,25 € under-charged per order |
| EUR, integration add-on active | 46,00 € | 17,25 € | 63,25 € | Correct, but untidy figures |
| EUR, manual price per currency | 46,00 € | 18,00 € | 64,00 € | Correct and deliberate |
The middle row is the one to look at. It is a 13% discount on the framing, applied to every euro order, decided by nobody. On a store selling 200 framed prints a month into the eurozone that is roughly 450 € of margin a month, and the only place it shows up is a slow drift in your add-on revenue per order.
The fourth row is worth noticing too. Once the integration is doing its job you still have a choice between accepting the converted figure and setting the fee yourself per currency. For a visible, standalone charge like gift wrap or framing, a deliberate round number reads better than a converted one and protects the margin at the same time.
How the Aelia Currency Switcher Fixes Product Add-ons Pricing
The fix is a small free plugin that sits between the two and passes add-on fees through the conversion layer. It is published as the Product Add-ons Integration for Currency Switcher and costs nothing.
Compatibility Status: Compatible, Requires Add-on
Requirements: Aelia Currency Switcher 3.2.x or later; WooCommerce Product Add-ons 2.5.3 or later; the Product Add-ons Integration add-on, available free of charge.
Tested and maintained by Aelia. This is a supported integration rather than a workaround, and it does not depend on a patch that a third-party update can undo.
Step 1: Activate Both Plugins First
Install and activate the Aelia Currency Switcher and WooCommerce Product Add-ons, and confirm each works on its own.
Step 2: Install the Integration Add-on Last
Order matters. The integration expects both plugins present when it loads, so install it after, not before.
Step 3: Test a Flat Fee in a Second Currency
Set a flat-fee option to a round number in your base currency, switch currency on the front end, and confirm the fee converts rather than staying the same digits.
Step 4: Add Rounding Rules
A converted 15.00 will arrive as something like 17,25. If you want clean numbers, set per-currency rounding in the Currency Switcher, or set the fee manually per currency.
Which Aelia Plugins Fit a Product Add-ons Store
| Aelia plugin | Tested with Product Add-ons | Why you might need it |
|---|---|---|
| Currency Switcher (£89.00 ex. VAT) | Fully tested, via the free integration add-on | The baseline. Converts add-on fees as well as product prices |
| Tax Display by Country (£69.00 ex. VAT) | No known issues, separate layer | Personalised goods sold into the EU need the right VAT treatment shown per country |
| PayPal Multi-Account (£39.00 ex. VAT) | No known issues, separate layer | Settle euro orders into a euro account instead of paying conversion twice |
| Prices by Country (£69.00 ex. VAT) | Not separately tested | Different prices per country rather than converted ones. Verify on staging first, because it also writes to the product price and can overlap with add-on pricing |
That last row deserves the caveat it carries. Prices by Country and Product Add-ons both influence what the customer finally pays, and the compatibility table tests the Currency Switcher rather than the whole Aelia range against every third-party plugin. If you need both, prove the combination on a staging site before it touches real orders. Our guide to regional pricing versus multi-currency explains which of the two you actually need.
Setup Notes and Known Limitations
Worth Knowing Before You Build
- Version floors are real. Currency Switcher 3.2.x and Product Add-ons 2.5.3 are minimums, not suggestions. Older combinations are untested.
- Converted fees will look untidy. Expect 17,25 € rather than 17,00 €. Rounding rules or manual per-currency fees fix this.
- “Custom price” fields need a decision. When a customer types an amount, be explicit about which currency they are entering, and label the field with the active currency.
- Test the cart, not just the product page. Add-on fees are recalculated when the cart is updated, so check the total after a currency switch mid-session.
- Do not run two currency plugins. A second plugin writing to the product price will produce intermittent wrong totals that look like an add-on bug.
Being plain about what is not covered: the integration makes add-on fees currency-aware. It does not make Product Add-ons multi-lingual, and it does not let you write a different set of option fields per country. If you need per-country option sets, that is a custom build rather than a setting.
How to Test Product Add-ons in a Second Currency
Five minutes of testing catches everything described above. The order of the checks matters, because each one rules out a different layer.
| Check | What to do | What a pass looks like |
|---|---|---|
| Flat fee converts | Set an add-on to a round base-currency figure, switch currency on the product page | The fee changes value, not just its symbol |
| Percentage fee is sane | Set a percentage add-on, switch currency | The fee is the same proportion of the converted price |
| Cart agrees with the product page | Add to cart, then switch currency while the item is in the cart | The cart line and the total both update |
| Checkout agrees with the cart | Proceed to checkout without changing anything | No change in the total between the two pages |
| Order record is right | Place a test order, open it in the admin | The order stores the currency and the converted fee, not the base figure |
| Caching is not lying to you | Repeat the first check in a private window with a cache-busting query string | Same result with and without the cache-buster |
The last row catches the one that wastes the most time. If a fee looks wrong on the front end but correct in the admin, you are usually looking at a cached page rather than a conversion fault. Our complete WooCommerce multi-currency guide covers the caching side in more detail.
Frequently Asked Questions About Product Add-ons and Multi-Currency
Does WooCommerce Product Add-ons Work With Multi-Currency?
Yes, with the Aelia Currency Switcher and the free Product Add-ons Integration add-on. Without that integration, flat-fee add-ons keep the same numeric value in every currency, so a £15.00 fee displays as 15,00 € rather than the converted amount. Requirements are Currency Switcher 3.2.x or later and Product Add-ons 2.5.3 or later.
Why Are My WooCommerce Add-on Fees Not Converting?
Because flat-fee add-ons are stored as a fixed number attached to the product rather than as a product price, so they never pass through WooCommerce’s pricing layer where conversion happens. Installing the free Product Add-ons Integration add-on routes them through it. Percentage-based fees are unaffected, because they are calculated from a price that has already been converted.
How Much Does WooCommerce Product Add-ons Cost?
Product Add-ons is sold on the official WooCommerce marketplace at $59.00 per year for a single site. The Aelia Product Add-ons Integration add-on is free. The Aelia Currency Switcher is £89.00 ex. VAT per year for a single site.
Do I Install the Integration Add-on Before or After?
After. Activate the Aelia Currency Switcher and WooCommerce Product Add-ons first, confirm both work independently, then install the integration add-on. It expects both plugins to be present when it loads, so installing it first can leave it inactive with no obvious error.
Can I Set Different Add-on Prices per Currency?
Yes. Rather than relying on automatic conversion, you can set a deliberate figure per currency so the fee is a clean number in each market, for example £15.00 and 18,00 € instead of a converted 17,25 €. This is the same argument as manual prices per currency on products, and it is the better choice whenever the fee is visible enough for customers to judge.
Does This Work With Extra Product Options Instead?
WooCommerce Extra Product Options by Themecomplete is also listed as compatible with the Currency Switcher, from Extra Product Options 4.0.2 or later. The difference is who maintains it: that compatibility is implemented and maintained by the plugin author, whereas the Product Add-ons integration is built and maintained by Aelia. Both work; the support path differs.
Sell Add-ons in Every Currency You Trade In
If your add-ons carry real revenue, the flat-fee conversion gap is worth closing before you open a second currency rather than after. The integration is free; the margin you are currently giving away is not.
Aelia Currency Switcher for WooCommerce
£89.00 ex. VAT, annual, single site. Includes the free Product Add-ons Integration add-on, a single-site licence, a year of updates, direct support from the team that builds the plugin, a 14-day free trial and a 30-day money-back guarantee.
Keep Reading on WooCommerce Add-ons and Currency
- Product Add-ons Integration for Currency Switcher, the free add-on itself.
- WooCommerce Multi-Currency: The Complete 2026 Guide for conversion and rounding.
- WooCommerce Product Bundles: Multi-Currency Bundle Pricing for assembled products.
- WooCommerce Dynamic Pricing: Multi-Currency Bulk Discounts for quantity discounts.
- Aelia Tax Display by Country for correct VAT on personalised goods.
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