Simple Past vs. Present Perfect

SIMPLE PAST A. It was so hot today that I wore shorts and a T-shirt. PRESENT PERFECT B. It was so hot today that I have worn shorts and a T-shirt.

A is possible. [FINISHED TIME PERIOD] You see "was so hot today". Today is finished. B is wrong. The day is finished.

SIMPLE PAST A. I had three lectures today and I still have two more later this afternoon. PRESENT PERFECT B. I've had three lectures today and I still have two more later this afternoon.

A is possible, but it's not the best choice. [FINISHED TIME WORD] You see "today". The three lectures are finished. B is possible, and it's the best choice. [UNFINISHED TIME WORD] You see "today", but you also see "later this afternoon". Today is not finished yet, so you can use the present perfect.

SIMPLE PAST A. We spent 200 dollars on food this month and there's another week to go before I get paid. PRESENT PERFECT B. We've spent 200 dollars on food this month and there's still another week to go before I get paid.

A is possible, but not the best choice. [FINISHED TIME WORD] You see "this month" and the spending of the $200 is in the past, but the month is not finished yet. B is possible, and it's the better choice. [UNFINISHED TIME WORD] You see "this month" and you see "there's still another week to go", so this month isn't finished yet.

Do you want a ride home? SIMPLE PAST A. No, I overslept this morning because my alarm clock didn't go off, so I need to work late. PRESENT PERFECT B. No, I have overslept this morning because my alarm clock didn't go off, so I need to work late.

A is possible. [FINISHED TIME WORD] You see "this morning", which is finished. B is wrong. The morning is finished.

Shall I make us some dinner? It's already eight o'clock. SIMPLE PAST A. No, thanks. I went to the dentist this afternoon and my mouth hurts too much to eat anything. PRESENT PERFECT B. No, thanks. I have gone to the dentist this afternoon and my mouth hurts too much to eat anything.

A is right. [FINISHED TIME WORD] You see "this afternoon", which is finished. B is wrong. The action is finished.

SIMPLE PAST A. I didn't read much of the report yet, but I have to finish it by the weekend. PRESENT PERFECT B. I haven't read much of the report yet, but I have to finish it by the weekend.

A is wrong. You see the word "yet" which means it hasn't even begun. B is possible. [NEWS / RECENT EVENTS] You see the word "yet" which means that the action hasn't even begun.