The first week of April saw a big retrace in both Commonwealth Bank of Australia (ASX: CBA) shares and Westpac Banking Corp (ASX: WBC) stock.

The S&P/ASX 200 Index (ASX: XJO) bank stocks came under pressure alongside the broader market after investors cottoned onto the fact the United States President Donald Trump wasn't merely bluffing about his global tariff campaign.

From market close on 2 April through to the end of trading on 9 April, jittery investors sent the Westpac share price down 8.6%.

And from market close on 3 April to market close on 7 April, CBA shares plunged 7.7%.

Now, it's never easy to wade in and invest $10,000 in quality sold-off ASX 200 stocks like CBA and Westpac before you know the bottom is in.

But the thing is, nobody can tell you if a company's shares have reached a bottom until after the fact.

So, if you followed Warren Buffett's advice to, "be greedy when others are fearful", and you invested $10,000 in each of the two ASX 200 banks at their recent April lows, just how much would you have today?

Let's find out.

Buying the April dip on Westpac and CBA shares

As mentioned, neither Westpac nor CBA shares were immune to the initial days of panic selling following Trump's tariff announcements.

But both ASX 200 bank stocks enjoyed a stronger rebound than the broader market.

That's likely because investors view the big Australian banks as a relative haven amid the global tariff turmoil. As very large companies, both bank stocks also enjoy strong buying from Aussie superannuation funds.

Now, on 7 April, CBA shares closed the day trading for $144.41. Meaning your $10,000 investment would have netted you 69 shares, with about $35 left over (not accounting for any potential brokerage fees).

On Monday, CBA closed the day trading for $166.93. Meaning the 69 shares you bought less than a month ago are now worth a cool $11,518.17. Or a gain of 15.18%.

Turning to Westpac, the ASX 200 bank stock closed on 9 April trading for $29.17 a share.

If you'd channelled your inner Warren Buffett and bought $10,000 worth of shares on the day, you would have received 342 shares, with just under $24 left over.

On Monday, Westpac shares ended the day changing hands for $32.45 each. Meaning those 342 shares you bought on the April dip are now worth $11,097.9. Or a gain of 11%.

As for what you might expect next from CBA shares, Australia's biggest bank is set to release its quarterly update on 14 May. Westpac reported its half-year results on Monday.